ANYWAYS Idiyuu is Hades and Persephone conspiracy:
Persephone is not from the Underworld. She is called back to the Mortal Realm eventually because she has to return. Yuu is literally from another world. They are not suited to Twisted Wonderland, and are nothing like Idia has ever seen. They have to go back eventually.
Hades is probably one of the few TWST boys to have a “canon” spouse (at least in Greek mythology, which Hercules’ Hades is obviously based on). On top of that, Hades and Persephone is the love story between death and life, isolation and abundance, ending and rebirth. Idia is a gloomy, pessimistic boy who has been condemned to be the keeper of the Underworld. Yuu is a kind, gentle prefect who has been there to help and has helped everyone they know, again and again.
Night Raven College has been in a ‘winter’ for all of its history. Everyone is hostile to everyone, no one wants to cooperate or work together, and every single person there has some ulterior motive. In comes Yuu, who is a breath of fresh air. A new perspective. A new season. They bring ‘spring,’ showing people that they can bloom. They can harbor feelings that aren’t cruel. They can do things that aren’t harsh. And slowly, they start to thaw. Flowers of friendship and something gentler bloom. Yuu is there to help pull the boys from their darkest moments to see the light again. Idia is no exception.
I think that the way Book 6 was set up makes Idia and Yuu seem a lot more meaningful honestly, though I'm probably reading way too into things lol. Yuu originally goes to the Island of Woe to save Grim. They don’t particularly care much about what’s going on with Idia—they just want to get Grim back. But then later, once they realize what’s going on, they do. There isn’t much, if any, personal connection to Idia’s overblot like there was with all the others. Yuu doesn’t have to do anything to help. And yet, they still do. Even after Idia basically kidnapped Grim, they still help him. They still try to end his winter.
Persephone, in many forms of the myth, didn't originally go to the Underworld willingly. But eventually, she came to love Hades, and they were happy together. Idia and Yuu have no reason to care about the other at first. But they eventually do, after everything that happens and everything that brings them together.
Hades and Persephone are in a constant push and pull. Persephone has to leave because if she stays, winter will never end. She does not want to leave, because she loves Hades. Yuu has to leave Twisted Wonderland, because they have a home beyond it that they need to return to. And yet, they don't want to leave because they love Idia. Idia doesn't want them to go, because it finally feels like spring again. But the seasons have to continue in their cycle, so what can they do?
Also, I think it’s really funny and really beautiful how Idia and Yuu’s first meeting was probably the Ghost Marriage event. This guy who thinks he has 0 rizz ends up having to be saved by some strange new isekai'd student and their gang of potential suitors before he gets his first kiss and promptly dies afterwards. Idia, the boy surrounded by death, is saved by the prefect who seems to be giving everyone a new chance at life. Imagine how poetic it’d be if Yuu and Idia end up getting married in the end, except now neither of them are going to die and they have the rest of their new lives together. There will be winter, but there will also be spring. The cycle of seasons will continue, but flowers will always bloom. They will always return to each other.