To be completely honest, I don't really think Kai will become a centipede monster. I knowww it's sad but my reason as to why is pretty agreeable I think.
Usually, whenever a character is transformed into a monster or just a non-human in general, it's always been about accepting and overcoming parts of yourself youd rather hide. When Zane was revealed to be a nindroid, he learned that the others would accept him as their brother no matter what, and soon enough, it became a strength for him. Literally, he gained his true potential shortly after. He no longer sees him being a nindroid separate to his identity. He went from Zane, a ninja, to Zane, the titanium ninja. He's still him, always will be, just shiny :)
When Jay was turned into a Venomari, it became a reflection of his insecurities, the parts of himself he tries to mask with flashy bravado and exaggerated stories, especially around Nya, who he had a massive crush on. It ended similarly to Zane, where Nya said he would accept him no matter what. Flaws and all. Knowing this, He was able to gain his true potential too. Realizing that being himself was far better than covering it up with glitter and foundation.
Then when Cole became a ghost, it was a tragedy. He no longer felt like himself, no longer saw himself as a person. Instead a living husk of his former glory. But, with the encouragement and unyielding support of his teammates, his family, he learned to accept this new body of his, as inhuman as it was. It symbolized trauma, and the strength it takes to see the good in every bad situation. It carries later into the show, where even though he's back to being a human, the scars are still there. They will never truly go away, but he learned to accept himself as himself, weird ghost scars and all.
Lloyd is the definition of grappling with identity. From being the son of Lord Garmadon, to becoming the legendary Green Ninja, then the ultimate Spinjitzu Master, then returning to simply being the Green Ninja, knowing hes half Oni half dragon, and ultimately just Lloyd? He carries many versions of himself, each with parts he struggles to accept. He’s the textbook case of change: from idolizing his father to fearing he’ll become him. It’s this internal conflict that makes it so hard for him to see himself as anything other than a ninja. While we see him begin to accept his identity later in the series, DR shows us that he still has some ways to go before he truly feels at home in his own skin.
Nya's transformation was also just.. unwanted, in my opinion. It was about doing everything you can to protect the ones you love, even if it hurts you. She's very similar to Kai in this regard, and it's very realistic that they share similar ideals when it comes to how they view their role in the team. Nya thought that merging with the sea was the only option, and faced with Jay unconscious after drowning, she had no choice. It was unwanted change, similar to Cole. This time, however, instead of Nya bringing herself back, it was the others who brought her back. It's a beautiful way to show that family will go through hell and beyond if it means protecting the ones you love.
What does this all mean, however? Why do these transformations matter?
Well, here's an answer. Despite everything, despite the hardships, they all came out of it better. They came out of it having learned something positive about themselves, even though it scarred them tremendously. Think of it like a caterpillar. In order to transform into butterfly, they have to break down and rebuild. In the end, the transformations ended up becoming a reminder to stay strong and steadfast. And it's nice that everyone had a moment like that.
Weeelllll.... not everyone.
Kai is the only one who hasn’t undergone a non-human arc, and that’s surprising, considering he’s probably one of the first characters you'd expect to experience one. With his personality and tendency to hide things from others in fear of being shamed or shunned, an arc like that would benefit him. Right?
This is where monstrosity comes in I fear. And not in a good way.
I think this series will be contradicting what those arcs symbolized. I think it will become the opposite to what the other ninja experienced. I dont think Kai will turn into a centipede creature or just any monster in general. No, not really. And that might be confusing, because In order to survive the land of the monsters, you need to become one yourself, right?
But i still think Kai will be the only one not to undergo a non-human transformation. Not because it wont happen, but because he doesn't need to. In fact, I think it matches the others perfectly. Everyone in the team became a monster physically, but they stayed the same. Same likes, same hates, just with different colored skin or lack thereof. They didn't change, their views didn't change, their morals didn't change.
But Kais did.
And Kai is.
He is a monster.
Maybe not physically, maybe not literally,
But mentally. But his actions were.
And that's enough, isn't it?