Regulus Black - Blog Posts

To make up for the angst that @read-reblog-repeat just posted that broke my heart, here is some smut that will be in the 10 bllu children book because the first chapter isn't finished but I really want to give you guys a peek.

Warning smut from here on out with trans Remus (Don't want or like, don't read simple)

Words: 412

Moans full of pleasure filled the bedroom, getting higher in pitch and volume as Regulus reached down to rub Remus’ clit, continuing to thrust inside him as deep as he could go, his grip on Remus’ thighs the only reason he wasn't sliding up the bed.

Regulus couldn’t stop from groaning as Remus scratched his nails down his back, creating gorgeous pleasure pain to course through his body. Regulus bit and sucked at all the skin he could reach, paying extra attention to the spots that made Remus most vocal. He soon found himself getting closer and closer to his orgasm, groaning through harsh breaths he forced himself to pull out, so he wouldn’t cum inside. Immediately scooting down the bed, wrapping an arm around his thigh, to keep Remus in place, and starting to lick and suck at Remus’ clit, before he could whine about no stimulation, every now and then pushing his tongue inside, as he jacked himself off with his other hand.

Remus was crying with pleasure, his werewolf senses making everything all the more sensitive. He suddenly felt Regulus tense and felt more than heard the loud moan he let out as he found himself climaxing. Unintentionally edging Remus as he stopped to catch his bearings, leaving Remus to cry in frustration because of how close he had been. Regulus was quick to shush him by using his now free hand to enter two fingers, instantly finding and rubbing at his g spot. Remus was so close, so impossibly close, with Regulus sucking, licking and fingering him, but just as he was about to cum, he stopped all his movements again.

Remus was about to yell at Regulus that he wasn't in the mood for edging kind of sex today, when his ears and mind started to cooperate. The sound of tapping at the window drowned out their heavy panting. Remus looked over at the window and saw an owl, looking a little frazzled, holding a letter in its beak. ‘I swear to Merlin if you get up to get that letter and don't get me off right now. I will slap you.’ Remus gritted out, hating how desperate he was feeling, when the moment had clearly been ruined. ‘What if it’s important?’ Regulus questioned as he rubbed his hands up and down Remus’ thighs. ‘Since when has anyone, ever, sent us anything important?’ Remus panted, squirming as Regulus’ hands got extremely close to where he wanted them.

This is what happened to most of James stuff throughout his years at Hogwarts

James: is that my sweater?

Regulus, looking down confused: no? I stole this from Barty

Barty: oh well I stole it from Evan

Evan: it's not mine, I got it from Panda

Pandora: I borrowed it from Dorcas

Dorcas: I got it from Marlene

Marlene: .... I may have stolen it out of Mary's closet

Mary: only because I stole it from Lily first

Lily: don't look at me I borrowed it from Remus

Remus: I only had it because I thought it was Sirius'?

Sirius: oh shit, I did steal that from you Jamie

Ok, I'm writing the 10 Bllu children, and I need names and as many plot points and sub plot points and personality traits as you can gather. They don't even have to be for the kids can be how the characters will react.

The story is going through all the pregnancies

Baby 1#: Sirius look alike

Baby 2#: James look alike

Baby 3#: Peter look alike

Baby 4#: Barty look alike

Baby 5# & 6#: Lily look alikes

Baby 7#,8#,9# & 10#: Remus look alikes

Also, characters that will be appearing are Remus, Regulus, Lily, James, Sirius, Peter, Marlene, Mary, Dorcas, Barty, Evan, and Pandora with Minerva and Poppy.

Please leave them attached to this so I can find them or tag #the 10 bllu children

Shout out to @read-reblog-repeat and @indigostation for collectively putting me onto the moonwater brain rot. I'm loving it here, and I can't stop thinking about the huge ass family of 10 look alikes that's been created.

The way I internally screamed at how much I loved this HC

Regulus would leave the most insane brusies and bites on Remus' waist, and he'd make sure they were in a spot where when the sweater did ride up, they were visible to all.

This would also make Remus really sensitive in this area, and he would have to force himself not to shudder and melt into a puddle every time Regulus grabbed and held his waist, another thing he was obsessed with doing.

Regulus seeing Remus' slutty waist, V line and light brown hair peaking above his pants while he tries to reach for something and his grandpa sweater lifts up and jerking off to memory for days until he can't take it anymore and pins Remus into a wall.

You can't give people these ideas like omg this actually killed me

big brown eyes, big brown eyes asking for permission near his crotch

Regulus Black you're so strong I would've made the Weasleys jealous of the amount of times Remus Lupin got BRED

Regulus x Evan x Barty

Sirius x James x Remus

Omegaverse Soulmate au

'You're Lucky.'

The voice startled Regulus from his current task of playing with Barty's hair, who was dead to the world resting on his chest. Regulus stared at Sirius for a second, who was standing in the doorway of Regulus' room. He turned his attention back to Barty because he had grumbled in his sleep, subconsciously missing the hand in his hair.

The thing is, Regulus knew he was lucky. Lucky that his soul mates were both pureblood, Slytherin, and came from respectable families.

When he told his parents who his soulmates were, he swears it was the first time he saw his mother smile genuinely. It scared Regulus a bit how excited she was to meet Barty. She hadn't even entertained the idea of letting Evan come to dinner as well, apparently believing that more than one Alpha in the relationship would take from Regulus' own dominance.

The entire dinner was spent with their mother demanding when Barty would be producing an heir, and Regulus just wanted to scoop him up and forget that he even entertained the idea of this dinner, let alone gone through with it.

But he knew he was lucky as he pulled the omega just that little bit closer, who let out a content purr in response.

'You're Lucky.' Regulus found himself shooting back before grabbing his wand and flicking the door shut in Sirius' face.

Sirius made his way back to his room, mulling over the words spoken. 'You're Lucky.' Sirius knew he was incredibly lucky. Lucky to have two amazing partners. James, a handsome Alpha who fit all yet at the same time none of the stereotypes for Alpha's and Remus, a beautiful omega who never seemed to know his own worth and has in equal parts a sarcastic and kind personality.

Sirius was lucky to have soulmates that were nothing like his blood relatives that would support him, that would cherish him. He found that he didn't care that his parents didn't approve of his soulmates like they did Regulus', he had learnt not to care about their opinion a long time ago.

So yes, he was lucky.

James potter was always the sun, but the truth is he never was. His dream? To fly towards it, and never look back. So when he had the chance, he ignored the warnings, he ignored everyone’s advice, and soared. And the sun the was beautiful, but as he flew closer, its beauty blinded him. He didn’t notice his back felt lighter, or his body was falling away. Only until I was too late did he realise that the sun was right Infront of him. All he had to do, was make them smile.

Marauders beetlejuice au??

Barbara & Adam Maitland -> James and Lily

Beetlejuice -> Sirius

Lydia deetz -> regulus

Otho -> Peter

Bernard(briefly mentioned, othos help) -> Remus

Charles & Delia deetz -> Walburga and Orion

Juno(the Maitland’s caseworker) -> Marlene

Jane butterfield (real estates agent) -> Mary

Shrunken head guy -> pandora

(I don’t know where Dorcas, barty or Evan could be mentioned but someone could make it work)

My introduction!

Hi I’m Louise, literally just someone who likes the marauders and wanted to get my thoughts out of my mind 🙏

I have a TikTok and insta, both handles are: tiny_pterodactyl

My TikTok has some crap edits so… be warned 🥀

My insta has some art, some marauders, some not, mostly jsut showcasing paintings, clay and drawings I have done

Marauders era characters as things my friends have said part 43

Sirius: *sends regulus a voice note of him yelling what the hell*

Regulus: is this why I keep hearing you scream what the hell?

Sirius: yeah

Regulus: your odd

Sirius: you’re, checkmate liberal

Regulus: die

Headcannons for the family lives of each marauders (please be reminded these are my headcannons and any hate will cause an argument from me 🫶)

James: happy loving parents but not all the time, families always have flaws the potters are just better at hiding them. He would argue with his dad a lot over stupid things but James never hated his dad

Sirius + regulus: of course the abusive Walburga and Orion BUT I like to think that when they were younger Walburga was kinder to them but was then placed under the imperious curse by Orion to keep her in line, and to discipline there children better

Peter: BIG family, kind of an opposite Weasley family, five sister and Peter is the only boy. I like to headcannon on of his sisters was deaf and non magic so she was less loved by her family but her and Peter were reallly close. Peter is the middle child, three older, two younger. His father is not in the picture, left when Peter was 7.

Remus: farm family, literally grew up on a farm and had like two horses, cows and chickens. His dad worked all the time and his mum was stayed home and took care of the animals. Remus was closer to his mum because he barely saw his dad but in the 6th year she got six and the year after they graduated she passed.

Marlene: child of divorce, (She jokes about it a lot) parents divorced on good terms but don’t keep them in the same room for long because they will argue. Has two older brothers that raised her when he parents were fighting

Mary: raised by her dad, only child, her mother passed away and severe complications during the pregnancy and birth. Her dad always would treat her like a princess but they did not grow up rich, her father balanced two jobs and taking care of Mary. He got a lot of help from grandma MacDonald

Lily: her and petunia were close, REALLY close and were all aware of them splitting apart after Lily was sent to Hogwarts. But I like to think they didn’t just, minimise contact. Petunia despised her so much that as soon as she could cut Lily out completely, that’s why she hated Harry so much. But deep down she still loved her sister,

Barty: absolutely despised his dad. (In a muggle au I enjoy him having severe religious trauma and that’s why he despised his dad so much, probs will write some short about this), his mum was completely corrupted by his dad and always listened and believed everything he said. Barty still loved his mum, he knew that she wasn’t really like that, it’s his dad’s fault.

Evan + Pandora: parents were very together but Pandora was raised as a princess, learning how to be a good housewife and a perfect mother, while Evan learned the “manlier stuff” (which I cannot think of right now so use your imagination). The Two grew up very differently from eachother, so they never had a strong relationship, but they learned bro be siblings over time

Dorcas: another child of divorce, probably why Marlene and her clicked so well. The only difference is that Dorcas parents divorced when she was really young while Marlene was older. Dorcas always favoured her dad over her mum but they both were severly flawed.

Marauder era characters as things my friends have said part 40

Barty: hey are you coming to hogsmeade tomorrow?

Regulus: I’ll make sure one sec

(Half an hour later)

Barty: it has been longer than a second

Regulus: this weekend right?

Barty: yeah

Regulus: ok one sec

(2 hours later)

Barty: bitch why do you say one sec and never reply

2 years.

It took regulus 2 years to figure out how badly he messed up.

It took regulus 2 years to tell the one boy, who finally saw who he really was, that he loved him

And it took 2 years for regulus to realised he messed up.

Regulus stood over the bowl, horcrux in hand.

In the background he could hear Kreacher telling him he had to leave.

In the background the sounds of inferni were moving towards him.

In the back off his mind was his sense of urgency, in the front was James.

It was always James, James potter. The love of his life, off dating Lily Evan’s the girl he liked forever.

They were always going to end up together, they were destined for eachother.

Regulus knew that when he started dating James but he wanted the potter all to himself and he destroyed it

James wanted regulus all to himself but from the very start regulus had stated that his family was always his priority.

The black family? Why would that be his priority, it wasn’t truly. He was just scared.

So now, 2 years later regulus is standing in the cave, handing the horcrux to Kreacher and screaming at him to leave

Now, 2 years later, regulus is screaming for James, trying to claw his body away from the hands of the inferni.

And now 2 years later, he feels a familiar warmth grab onto his hand and pull.

2 years later he’s in the arms of James again, but at what cost?

I’ve decided to share with you guys my short story for English assignment. I got an A- on it so I hope you all like it 😁

A Universe Apart

James wandering around felt useless, his brain spun with various thoughts. Throughout the last few hours, he had found himself in many places that can’t even exist on earth. He had been walking endlessly and painfully through a dark and creepy forest for a while now. A cloud of fog surrounded him, corrupting his vision making him barley able to see. His body limply wandered around the forest; he was certain he had been past these trees before. He could barely think straight, his mind racing with every possible reason on how he ended up here. James knew that at any second, he was gonna be chased by some monster. While he wandered, his obstructed vision stayed peeled for any signs of human life, any sign of Regulus. Because one second, Regulus was there and the next he wasn’t, James practically broke down completely when he disappeared. He couldn’t function without Regulus. He snapped out of his train of thought and stood in place, he groaned loudly and spun around trying to find something different, but every single path led to the same place. James rubbed his eyes, keeping his hands there for a few moments, hoping that when he opens them, he’s back in his apartment. Where Regulus is standing in front of him, yelling at him. James would much rather go back to Regulus yelling at him then losing him. When he finally opened his eyes, he was disappointed to still be face to face with trees.

‘This doesn’t make sense’ He thought. One second, he was having an argument with Regulus and the next Regulus was gone, and moments later James was gone too. He felt his body fume, transporting to different places at random points of time, it doesn’t make any sense.

“Jesus Christ,” he mumbled. He slipped his glasses off for a second, taking this moment to rub his eyes again and sigh, once he placed them back on, he spotted something unfamiliar in the distance. A tall figure, he could barely make it out, but he was certain it wasn’t a tree. James looked around for any other signs of life, when he looked back the figure had ventured forwards. It was almost half the height the trees were, and it practically towered over James even though it was still so far away.

“What on earth?” he whispered, the figure stayed still, continuing to stare at him. James eyes wandered for a second to check his surroundings, when his eyes went back; the figure was closer. He could see it clearer now, tall, skinny and pale, its body veiny and slimy with a large smile plastered over its face. James body straightened and grew tense, he realised quickly that as soon as he looked away it was going to move closer.

James chuckled to himself, he did say there would be a monster. He decided looking away was the best choice. Whatever it was, it was either going to have to kill him or help him. When he looked back the figure was standing right in front of him, if James moved even an inch he would be touching it. James was at eye level with the monster’s knees, slowly James looked up, its face was look down at him smiling. James carefully stepped backwards, keeping an eye on the monster at the same time. He rolled his eyes; his breathing grew heavy and his eyes furrowed.

“I said,” He huffed “I’m not DEALING WITH THIS!” James’s outburst seemed to send him to a rocky, snowy mountain range. A chill ran down his spine immediately as he rubbed his hands together then crossing his arms to try to bring some form of heat to himself.

“Oh my god!” James chuckled; he couldn’t believe it. A burst of hysterical laughter fell out of his mouth, he really couldn’t believe it. James looked around, Jagged mountains on the brink of falling surrounded him. As he turned around trying to find something other than mountain, he spotted something in the distance. Something out of place, something that wasn’t rocks and snow, it wasn’t too far so it made it easy to identify. A person. James felt a wave of hope wash over him; he started running. Running towards whoever it was, James prayed that he wasn’t going to be sent somewhere else or fall into a crack in the mountain. Although the person wasn’t that far away, he felt as if he was running forever. As James approached the body, he noticed immediately that they were… dead. James sighed, he was still alone, without Regulus, but now he knew that other people have been stuck there too. James examined the body; they were already half decomposed, and the stench was indescribable. James almost walked away until his eyes landed on a shiny object, a large emerald ring. James felt his stomach drop. He slipped off the ring and looked back at the body.

“Regulus…” His voice barley above a whisper, James continued staring at the body. His partner was dead. James blinked and found himself somewhere else. He looked down at the ring that was in his hands. The ring that he picked out without a second thought, the ring that caused their fight. Regulus was wearing the ring, he said yes. James let out a painful sob, he slipped the ring into his pocket. James looked around him, the place was a long empty field, the grass dying, the sky completely grey. In the distance large building, bikes, trees and other various objects were sinking into the ground. James started walking. His mind racing with the last memory he had with Regulus.

“James,” Regulus sighed “why should I say yes?”

“Because I love you,” James pleaded, his voice cracking “and I can’t imagine being with anyone else.” He was practically on his knees, his eyes blurry and watery.

“There are so many other factors to think about!” Regulus retorted, his own voice breaking.

“Forget the factors! Why can’t you just love me?” James finally snapped; Regulus flinched at the sound. A wave of guilt washed over James; he started to mutter apologies.

James kept walking; he walked until his body physically couldn’t anymore. He collapsed onto the floor, his legs screaming in discomfort. The pain of losing the only person who ever truly loved him, all hitting him at once. James curled into a ball and sobbed, clawing at the grass, screaming and crying, a knot forming in his stomach. Slowly the ground sunk, like the buildings and bikes, James was becoming submerged by the ground. He didn’t try to get out. He knew he was lost without Regulus. The pressure began to snap James bones, the sound of crunching filling his ears, he screamed in agony. All James could do was remember regulus, his favourite memories.

“Did you know that when the body dies the brain stays active for another 7 minutes?” James said, bouncing towards Regulus.

“That’s not actually true, there’s no scientific evidence.” Regulus chuckled, letting James’s arms wrap around his waist and bring them together.

“Well even if it isn’t true,” James smiled “I’d still be thinking about you before I died.”

I wrote a Jegulus fanfiction for my English short story thinking my teacher wouldn’t know what the marauders were but she came up to me giving me feedback and said “maybe this is just my fanfiction brain” and then she said “maybe discuss some of there years at Hogwarts” and I genuinely have no idea what I felt in my moment but afterwards I could not stop giggling

When regulus told Sirius he was trans, Sirius practice told James immediately. Sirius only told James so he could protect regulus. James wasn’t a violent person but when it came to someone he loved he would do anything to protect them. At the time Sirius didn’t know James loves regulus, at the time Sirius didn’t know regulus had already told James, had already asked him to protect him, indirectly of course. Sirius only figured it out when James punched someone for insulting regulus, Sirius only figured it out because James would do anything for someone he loved.

I’ve made one of my friends who doesn’t know shit about the marauders read art heist baby during a cyclone while her power is out, I haven’t gotten any confirmation if she enjoys yet but once I do I will update.

James was actually really good at singing, he just never showed it because he thought it was embarrassing. The only person who ever heard him sing was regulus, completely by accident of course. Regulus was a bit late to meeting James at the astronomy tower one night, James decided to take the time alone to sing aloud a song he had stuck in his head (he always had something stuck in his head). Regulus was mesmerised by the sound and ended up being later than he expected, just because he was standing listening to James sing. James from then on would sing to regulus, whether he was having a panic attack or just sitting together and regulus asks, James would sing for him.

After they broke up, regulus found himself mumbling songs that meant something to him and james. James however, never sang again.

Marauder era characters as things my friends have said part 31

Regulus: I’m listening to the wicked soundtrack full blast in my headphones

Pandora: movie soundtrack? Or the original

Regulus: movie… I like Ariana grande

Marauders era characters as thing my friends have said part 22

Barty: why do these chips look like ASS!

Evan: what the fuck

Evan: they look like regulus’s skin colour

Marauders era characters as thing my friends have said part 20

Regulus: naming my notes is getting more difficult, this one is just called let’s fuck around and find out

Barty: what’s the note?

Regulus: I don’t know bro, wanna fuck around and find out?

Barty: yep, without around and find out

Marauders era characters as thing my friends have said part 17

Pandora (in a letter to regulus over the holidays): yo bitch, you should come to my place on Wednesday. And if your parents say no, backflip to assert dominance

Marauders era characters as thing my friends have said part 12? I think.

*regulus removed a silencing charm he had on Barty and evan*

Barty: whew, that was scary

Evan: yup

*places silencing charm back on them*

(This was in my gc when I removed there ability to talk 😃)

Marauders era characters as things my friends have said part 4

James: are you having family issues?

Regulus: no I’m having criminal issues.

Associating Kate Bush’s Army Dreamers with the Black brothers fills me with a sort of pain I can’t even describe.

I’ve always imagined it in Sirius’ perspective, because despite the fact they both had parents we know deep down they are not the ones who raised the two. Sirius has been a father figure to Regulus since he could remember, and Sirius was most likely taken care of by a house elf or nanny.

Regulus turning to the Dark Lord didn’t change that, he would always be Sirius’ little brother- the one he tried to pull away with him when he realised how bad his parents views actually were. When he suspected Regulus of being a spy for The Order.

His death broke a part of Sirius irreparably, when he heard the news he probably couldn’t believe it. Even if Dorcas was likely the one who told him. No one would want to believe their little brother, the boy they raised, is gone.

Only because he got Involved with a war neither of them wanted to be a part of, and not to mention dead because of it. It was Regulus’ dream to be a part of The Order, Dumbleldore’s army. He didn’t want to be defined by bigotry anymore.

Regulus was an Army Dreamer, and if Sirius could turn back time he’d crush that dream beneath his feet and take them away from it all. Regulus didn’t make it to his 20’s. His life was wasted for the ‘greater good’. They were child soldiers, not because either wanted to fight.

They were soldiers because they had no other people to give their lives to.

@n0r

me looking at a character that's acting all tough but one listen of Class of 2013 (Audiotree Live) would send them into a coma they would never recover from:

Fun Fact when Regulus died Sirius barely moved, barely ate, barely looked at anyone or anything for days besides the only picture he had of Regulus as a child, smiling and clutched it to his chest while whispering "my baby, my baby, my baby" on repeat to himself as tears streamed down his face.

(And Remus could do nothing but hold Sirius as his heart broke for him and James)

I come to you with this question because, having read all your other metas, I think you'd be the right person to ask. Id love to know what you think about Regulus because I have a very hard time understanding his character. Partly because of fanon characterization of him makes him seem like some secret rebel against Voldemort and partly because I just can't really understand any of his motivations. But regardless, I think what we know about him in canon is so interesting - i just can piece it all together. I'd love to know what you think!

(Sorry for the longish ask)

thank you very much for the ask, @hauntingpercival! regulus is a character i also find a bit of a mystery, and so thinking through this answer was really fun.

i'll start by being clear that i'm certainly not a regulus fan. by which i not only mean that i don't vibe with the fanon!regulus of the marauders fandom, who is essentially an original character - and you can read my views on jegulus here... [spoiler alert: i do not back it] - but that when he appears in my own writing in ways i'd like to hope feel influenced by his canon form, i always find myself focusing on aspects of his character which are rather unlikeable.

there is a little bit of a discourse-y reason for this, which will be pertinent to the rest of this answer...

i really don't like the sort of "omg aristocracy is so hot and sexy and interesting" tropes which are so prevalent in writing around the black family. this is firstly because i don't think that aristocracy is in any way these things - and i find it distasteful to imply otherwise - which is because i'm a prole who lives somewhere still bearing the scars of british colonisation who also went to the sort of university where one sometimes encountered aristocrats and they were all cringe and unbearable.

but it's also because it's not - and i will genuinely die on this hill - an accurate reflection of how the blacks are presented in canon. not only does it take sirius' comment that his parents considered themselves "practically royal" to be a statement of fact [sirius is quite clearly taking the piss out of his parents' pretensions], but it also misses that the purpose sirius' discussion of orion and walburga's politics serves in the narrative of order of the phoenix is to show how mainstream their blood-supremacist views were.

sirius tells us that his parents were not death eaters, but that they nonetheless thought voldemort's overtly sectarian political aims were correct. in this, they hold the political views order of the phoenix emphasises belong to cornelius fudge - unimaginative, deferential to the class system, casually prejudiced, and so on. orion and walburga function as a way of showing us just how entrenched the death eaters' manifesto is, how close voldemort came to winning the first war, and what an uphill struggle the order faces to unravel the roots blood-supremacy has in the wizarding world.

[and they also show that the baffling vibes of grimmauld place - while these are made worse by it being three different gothic literature tropes in a trenchcoat - are wizarding norms, rather than evidence that the blacks were uniquely immersed in dark magic. the decor at grimmauld place - and the family's collection of dark artefacts - is the same as that found in malfoy manor, even at a time when lucius malfoy is considered eminently socially respectable. this is a point we will come back to...]

i think, then, that it's crucial to approach regulus not as a swaggering aristocrat, but as someone from an upper-class background which - while still posh, rich, inferring enormous social capital, well-connected - was unremarkable within the circles in which he moved.

by which i mean that hogwarts is based on real-world institutions - britain's elite boarding schools - which are so exclusive and expensive to attend that the student body are from a class-background which seems inhumanly exclusive, affluent, and powerful from an outsider perspective [i.e. from the perspective of someone from the majority middle- and working-classes] but which seems completely normal within the student body itself.

[i.e. nobody at eton with princes william and harry will have been astonished to have been at school with a royal, because they will have been familiar with their social circles, cultural experiences, level of wealth, and expectation of knowing someone with considerable social influence from childhood.]

while hogwarts appears to be a state-funded school [although it also expects an enormous amount of financial investment on the part of parents - such as buying all the textbooks], the fact that its real-world parallels are so elite [and, therefore, come with a specific "look" in the british cultural imagination] means that the student body is incredibly well-heeled and working-class students stand out enormously in a way very rich students do not. hogwarts also exists - like real-world elite schools and universities - as a way of propping up the status quo of the class system by which the wizarding world functions. its pupils have an expectation of procuring jobs in the civil service and other influential professions - using not only connections established at school but connections they possess through their [male] relatives. many hogwarts students we meet in canon are related to someone who occupies an elite position in the wizarding executive or is otherwise socio-politically influential.

at school, then, regulus would have been completely, perfectly average in terms of social position. i also like the idea of him as perfectly average in terms of intellect - and as a good, but not exceptional, seeker. this provides a really interesting point of contrast with sirius, who - while he's also not socially unusual in terms of class [and i will never vibe with tropes like him being followed by whispers going "omg, he's a black, that means he's important"] - stands out in that he's the first black in generations not to be in slytherin, that he's precociously intelligent, and that he - and the rest of the marauders - are class clowns and show-offs.

and i like the idea that this would give regulus a desire to stand out - to be considered the most important person in the whole school. we can get a hint of this in canon - the picture of sirius and his friends harry sees in deathly hallows is immediately contrasted with a picture of regulus sitting in the seeker's position in the team photo. the seeker who acts alone.

and i think this desire for notoriety is what drives him to sign up to become a death eater - that he decides he's sick of having parents with the perfectly normal level of social influence and a brother who is more popular than him, and that he thinks that he's cleverer and more worthy of attention than everyone else in the castle and the world better start showing it.

[and i've never bought - i'm afraid - the idea that he and sirius are close. it's clear from canon that regulus had no issue being thought of as "a much better son" than sirius, and that he colluded with his parents against him. sirius can love him - and miss him, and regret how they were never able to repair their relationship - but i don't think this means that he feels he's lost a bestie.]

that he holds sincere blood-supremacist views is a given - because within the world in which he lives, these are completely normal and held completely casually [i.e. that slughorn is shocked lily could be muggleborn because she's clever]. the more virulent expression of these views - saying "mudblood", etc. - is clearly considered ill-mannered, but not something which might have any real impact on one's social standing [draco malfoy uses the term with impunity while at school, and nobody ever considers that informing a teacher of this would result in him being punished; equally, nobody from the crowd who witness the event reports snape for calling lily a mudblood].

and so i think it's clear that he becomes interested in joining the death eaters - and starts putting together his terrorism pinterest board - because his mainstream belief that being pureblood is better crashes into his desire to be special to form a conviction that riding the coattails of voldemort's ostentatious malevolence is the way he can become famous.

[in this, he is very like snape.]

my assumption is that regulus is one academic year below sirius, meaning that he was born in 1960-1961. my assumption is also that he receives his dark mark while still at school - probably at some point in his newt years [so the academic years 1977-1978 and 1978-1979].

the standard view - expressed vehemently by various order members in half-blood prince - is that voldemort has no interest in death eaters who are still at school.

the order is wrong about this, obviously - not only when it comes to their refusal to accept that harry's right about draco malfoy being marked, but also in the fact that several of the death eaters who are very young at the end of the first war, barty crouch jr. [who is still young enough to be described as a "boy" in 1982 at the earliest], chief among them, must have been taken on by voldemort prior to graduating.

but it seems fair to say that admitting teenagers into his inner circle is unusual for voldemort, especially when those teenagers don't really offer him anything useful. crouch, for example, could be put to work informing on his father's movements. regulus is - as i've said - just ordinary.

and so my view has always been that regulus is marked by voldemort as a favour to bellatrix. i think this partially because i'm bellamort trash, partially because i think it's a nice narrative parallel between regulus and draco [who are very similar] to have bellatrix be responsible for regulus' recruitment when she's canonically vociferously in favour of draco's, and partially because realising that voldemort thinks of him as just some guy who warrants [essentially] a pity dark mark would be a big blow to regulus' conviction that joining the death eaters would make him impressive.

[i also think regulus is recruited before 1978 because i think there has to be a shift in voldemort's modus operandi at about this point, in order for the fact that sirius says that his parents got cold feet about what the dark lord was prepared to do after regulus became a death eater to make sense. my view has always been that voldemort's violence prior to c.1978 overwhelmingly targets state institutions and people connected to them and/or people with known anti-voldemort political views, meaning that ordinary citizens can regard these people being killed or injured as reasonable risks of their jobs and/or behaviour. and then that after c.1978, the dark lord begins targeting civilians - including upper-class pureblood civilians - indiscriminately, which makes his casual supporters start to waver a bit.]

so, let's suppose that regulus leaves hogwarts in june 1979 and finds himself expected to participate as a full death eater, after having been let off all the dirty work by virtue of being at school...

as i've said, regulus has an enormous number of narrative parallels with draco malfoy. and i think that the best way to think about him is to write him as sharing draco's canonical attitude to voldemort's cause - that he believes whole-heartedly in the message of blood-supremacy the dark lord promotes and that he has no problem with people he considers subhuman [mudbloods and blood-traitors] or unimportant [faceless families massacred in their own homes] being subjected to violence in the name of that message, but that he lacks the character traits necessary to perform that violence himself, to see it done to people he likes, or to witness what it actually involves versus the image he has of it in his head.

and so i imagine he starts struggling pretty quickly with the fact that being a death eater isn't quite as easy as he thought it would be when he was making voldemort fancams on tiktok. and that part of the reason he's primed to turn against the dark lord is because of the tension he feels warring within him at the fact that he's still a blood-supremacist, still desperate to be important, and yet growing disenchanted.

i don't however, think this is why he does what he does... so let's get into that:

why does regulus turn against voldemort?

let's be clear about one thing - regulus turning against voldemort has nothing to do with him having some sort of damascene conversion against blood-supremacy.

[or, at least, that's what i think.]

the outline of regulus' defection that we get in canon goes as follows:

voldemort asks someone to lend him a house elf. we know that regulus volunteers kreacher, because he told kreacher so - and so i imagine voldemort mentions at a meeting that he wants to procure an elf [although, of course, he doesn't elaborate on why] and regulus immediately jumps up and says "pick me, my lord" because he sees this as an opportunity to get voldemort to finally notice him.

his assumption must be that voldemort will use kreacher for a purpose which is considered normal in wizarding society - i.e. that he will require him to do something akin to domestic service, perhaps preparing potions ingredients.

it evidently does not occur to him that voldemort would transgress this social boundary and harm kreacher. not - to be clear - because i think that regulus was some kind of abolitionist legend, but because we see several characters express the view in goblet of fire that how barty crouch sr. treats winky is his own business, and that it is impolite for respectable wizards to comment on how anyone else treats his slave. this sort of social behaviour will have a second part - that it is impolite for respectable wizards to treat anyone else's slave in a way which goes beyond what wizarding slaveowners see as normal.

or: that it's fine to be lent a slave to serve you, but very much not fine to nearly kill that slave [someone else's property!] for your own gain.

kreacher informs regulus what voldemort asked of him, which makes regulus suspicious about what the object voldemort deposited in the cave was. regulus then decides to investigate.

kreacher tells us that regulus goes away for an indeterminate period of time and then returns to grimmauld place "disturbed in his mind".

dumbledore claims in half-blood prince that voldemort appears not to wear or display the objects the horcruxes are made from after he turns them into horcruxes. i think we can agree with this or not without it affecting the story - i quite like the idea that voldemort doesn't make the locket until the later 1970s [maybe after the murder of dorcas meadowes, the only person in the first war other than james and lily to have canonically been killed by him personally], but we can also say that he might have worn or displayed it when it was already a horcrux. certainly, regulus must have seen the locket - either on voldemort or somewhere in his lair - and, after kreacher tells him what happened, he goes to see if it's still there.

when he discovers it isn't, he comes to an important conclusion. one which requires a little detour...

how does regulus know what a horcrux is?

i complained at the start of this answer about the black family being portrayed as unusually immersed in the dark arts - rather than some sort of familiarity with the dark arts being perfectly normal for people of their social class.

and i am sure that you might think I'm about to have to eat my words, since i'm not going to try and deny that regulus was able to identify a horcrux all by himself...

but, actually, i'm just chucking malevolently at the opportunity to clamber onto my soapbox and say:

horcruxes are canonically not magic which only a handful of people know about. where voldemort goes beyond the theory of horcruxes which a wizard of regulus' class-background would be familiar with is that he makes seven.

this doesn't mean - to be clear - that i think it was ever common to make a horcrux [i don't think the wizarding world is quite that lawless...], but that it was reasonable to know they exist, in the way that we might have some general understanding of something macabre - like techniques for disposing of a body - which would enable us to suspect if we saw a neighbour behaving strangely while doing one of those things...

after all, slughorn can suggest [even if he doesn't believe this is what he wants to do] that voldemort could justify his interest in horcruxes by using the excuse that he's working on a project for defence against the dark arts.

that harry, ron, and hermione don't know about them is a result of a combination of their own lack of interest in the theory of the dark arts, the information blackout instituted by dumbledore at some point after voldemort graduates [and my theory as to why dumbledore hates horcruxes even in the forties? grindelwald made one - hence why dumbledore is so hopeful at king's cross that the rumours of his repentance might have been true...], and the fact that they don't discuss their mission with anyone [tonks, kingsley, and moody, who literally have to specialise in dark objects as part of their jobs, would one hundo have known what a horcrux was].

[what they would not have known is what voldemort's horcruxes were likely to be made of and where they were likely to be. it's this - rather than the idea that horcruxes are completely unknowable magic - that is why it has to be harry in charge of hunting them down: he's the only person in the series who knows voldemort well enough to realise that, for example, he'd have hidden one in gringotts because of his jealousy at being excluded from this pillar of wizarding normality.]

so, regulus has a little rummage, works out the locket has disappeared, and has no trouble - especially because voldemort mentions in goblet of fire that he'd told his death eaters he couldn't die [which regulus might not have thought was him speaking literally] prior to 1981 - guessing what it's being used for.

and so, regulus turns against voldemort.

and i think that he does this because the horcrux makes it impossible for him to pretend any longer that voldemort's aims are - when the ministry is forced to the negotiating table by his paramilitary activities - an oligarchy in which upper-class pureblood families benefit and muggleborns and blood-traitors become second-class citizens, but which doesn't deviate too much in terms of its overwhelming norms from the way wizarding society functioned at that time. instead, he is confronted with the undeniable fact that voldemort intends to reign forever as an immortal absolute monarch, and that he has never had any intention of elevating regulus and people like him to the positions of importance he so craved.

[we see something similar happen to draco, whose increasing fear of voldemort throughout half-blood prince and deathly hallows is clearly driven by him realising that voldemort isn't joking when he says that he'll kill him and his parents unless he obeys orders, but is joking when he says he'll be considered a valuable servant should he manage to kill dumbledore...]

and so his death - and his threat to destroy the horcrux - is a repudiation of his beliefs. but, specifically, it is a repudiation of his conviction that voldemort was a primarily political figure who would act as a champion of the pureblood class-system. it's him recognising that voldemort would not stop with a takeover of the ministry - he would kill and kill forever, concerned only with how much further he could venture beyond the norms of magic.

[James and Regulus making out]

Sirius, walking in: Hey Prongs— Wh—

Sirius, yelling: Get your hands off my brother you fuck!

James: [raises hands]

Sirius: Now, what the the actual hell is—

Regulus: [also raises hands]

Sirius: Why the fuck are YOUR hands up, Reg

Regulus: I—

Regulus: I didn’t know which brother you meant