Warning: Spoiler
We are all aware that Yuu did not speak too much, and if they do, whatever dialogue Yuu picked, the result is still the same. Yuu will still get strung along and deal with the troubles and the overblots.
One may not think much of the part they play, merely a person that talks on the other side of a screen where the characters wouldn't heard you.
However, small and worthless as it looked, Yuu's words and existence are significant enough to push the story we all know.
Without Yuu, Grim will never attend NRC. Ace will not go to Ramshackle Dorm and consider Yuu's words to apologize to Riddle, nor will he have that kind of friendship with Deuce. Riddle's tyranny continued, Trey still remained the same just like Cater, and their relationship with the rest are within arm's reach.
Who will take the role of an investigator when there are accidents during the Spelldrive Tournament and foil the Savanaclaw plan?
Who will save them from the repercussions of striking a deal with Azul? Jamil succeeds in going through his plan and reaching his goal but not without a cost. Nobody will be able to return Vil's appearance back to normal if Malleus were not invited. The same goes for the rest.
That is the world without Yuu. Only if Yuu exists will the story move forward where everyone is saved and has come to peace with their issues even if the first meeting wasn't that great.
However, that does not mean everything will turn out okay if Yuu exists. It's all about their personality and how the people favor them.
Everything turned out to be even worse than ever if the others dislike Yuu, who is indifferent, or Yuu has the aura and personality that people immediately hated them on first sight.
There's something irritating when they were looking at Yuu. Something that caused them to loathe Yuu even though Yuu hasn't done something that garnered their unreasonable hatred. Plenty of people here are villainous in some traits, from tyranny down to pure selfishness.
However, although Yuu had not shown these traits, one can agree that Yuu is simply… dislikeable.
Just that feeling alone, and they avoided Yuu. Some mocked them, but Yuu did not take it to heart.
Yuu does not understand how they are disliked. They mind their own business, mindful of others, and only joining when it needs to. Yuu tried to be considerate and laying low. It's people's fault who are refusing to understand them.
Grim was not as close, preferring to look down at Yuu and make them work. Ace and Deuce were not Yuu's friends; the statue did not burn nor did the expensive chandelier ever fall down. Ace merely mocked Yuu and passed by as they swept the floor, and Yuu never met Deuce.
Yuu is alone during break time, and Trey and Cater never get to know them. Maybe Trey did send pitiful glances, but that's it. There's no need to get involved if you don't know them.
Riddle, however, knew Yuu but only by face and a title "magicless janitor". He got a worst impression of Yuu during the ceremony, and they never talk to each other after that.
Yuu and Grim were never present during the unbirthday party; the Mont Blanc was never made, and no one knew about Riddle's issue of how he came to be a tyrant.
Nevertheless, overblot happened, and it went downhill.
There were deaths and the wounded, and the hierarchy changed. Trey became the 'Queen of Heart', and Cater his right-hand man card soldier. Trey blamed himself and the people that contribute to Riddle's overblot which then bred dissonance and defiance amongst the card soldiers.
The dorm known for its countless rules became lawless; anarchy became the norm.
Yuu did not bother. As sad as it was, it was not their business which making people capable of sympathy dislike and avoid them even further. Yuu is a magicless janitor after all; it was also their job to clean up, and Yuu can't afford to feel when he's busy working.
Spelldrive tournament still continued, and most of the greatest players in Heartslabyul Dorm joining the tournament were almost non existent. The accidents of people falling and accidentally hurt themselves still happened and Yuu, despite being a janitor, was asked to investigate and found nothing due to people being uncooperative.
Nothing was done to oppose the plan Savanaclaw came up with. Although the intended target is not affected, many were still injured during the stampede. No one was able to point out the culprit behind this.
But still, overblot occurred before the audience, and on the screen across the world the moment Savanaclaw lost to Diasomnia.
Leona was saved after that in just a matter of time, but he was ashamed. Not because he was thinking of Malleus' downfall and Malleus had saved him despite everything, but rather because he was being exposed to the world. The eyes of his lackeys that trusted his words lost its gleams, and Leona was alone.
He is but an undignified cub unworthy of the throne.
He tarnished the school name and the royalty. He did not become a king, nor did he become part of the family, and instead, he was expelled from school and banished from his pride, never to be seen again.
That is the only mercy they can give, to let him run and live. But they will not forget what they cannot forgive.
The housewarden position remained absent. Lying became unacceptable. Selfishness and unruliness grew. Despite that, they are all a pack and they don't need a king at all.
Ruggie had to resort to scamming and stealing others' food, and Jack's sense of justice wavered at the sight. The scale slowly leaned towards a grey area, and before long, Jack found himself unbothered by the mess around him.
Gradually, once everything stabilized, the exam month arrived, and almost all students got caught in a net that Azul threw strategically. Grim was no exception. He made a deal with him about something, and Yuu could have left him behind, but Grim was vital, so Yuu had no choice but to save him.
Yuu saved only Grim, no one else.
They got off rather easily with a few challenges here and there, and Azul did not overblot, but plenty of students either dropped from fatigue or developed resentment to the point of overblotting. Naturally, everything comes to light.
Yuu did not bat an eye why Azul was forbidden to do business and anything that required him to steal everyone's power. Unfortunately, Azul does not react well. Forbidding him all of these means his power is taken away.
He instantly overblotted. Nobody is able to fight back as Azul was stronger from all the power he stole. But using those powers eventually leads to getting his life force drained, and that's what happened.
It does not end there sadly. Although Yuu was not dragged into the future overblots and the mess that comes with it, Yuu was still involved in cleaning the aftermath.