Canon-compatible reasons Izuku is like that in 431
still doesn’t believe he can be a hero without a quirk
nothing changed when he WAS a hero so he’s better off helping the next generation learn to be decent humans and heroes
Thinks he failed and the world doesn’t need him to keep trying when the consequences are that bad
Depressed as hell and needs therapy
Locked so deeply in the closet he doesn’t even know he’s stuck there
Misunderstood what Katsuki was actually asking and failed to communicate why he was saying no
Genuinely does not realize what he means to everyone, still, even now
Feels like he’s done nothing but burden Katsuki and take advantage of Kats’s “guilt”-motivated kindness
He wants to prove to Katsuki that he can be his equal again first, before being his partner (even if Kats already knows this Izuku thinks he has to prove it to be worth something)
He genuinely doesn’t have time right now, let him finish the school year and get up to speed again
Realizes he needs to make the rounds to all his friends and let them know they’re important to him, starting with Ocha and ending with Katsuki
They’re actually already together, but it’s a secret
(My personal favorite) Toga replaced him in a misguided attempt to get closer to Ocha