Giving in to temptation or breaking one's own rules is rape as well now. Changing ones mind a day after too, or having a guilty conscience - all rape. Californistan brainrot is spreading wild. Point me to the page showing he "didn't want to". Not the one in your head canon, one that is actually drawn by the author, the ONLY authority on what is and isn't happening
Have you ever read or even heard of those popular smut novels for women? While it's iffy at the very least in RL, in said literature the saying " it's not rape when they like it" is accepted common sense. So yeah, it not only exists, it's wildly popular. It's called fiction. But since there was no rape to begin with ....
If he gave in when he was half-asleep and drunk/hangover after being given (illegally because he's too young for that in Japan) alcohol in first time in his life by his teacher, then he was in fact being raped. She didn't just seduce him and make him break his rules on his own, she went at him only when he was in the worst state to think straight and keep to his rules. That's the rapist's way. "Oh this girl is the kind that refuses to put out before marriage, well she's a freshman that never had alcohol before, we'll get her drunk on welcoming party and then she won't protest as we take rounds" is the kind of rape that happens in real life.
As for those smut novels, they're basically porn, and they usually try to be only slightly "forced" by various tricks, those that don't and go full "hot rapist made me his willing sex slave" are hardcore fetish stuff and not as popular. But this series isn't treating it as hot dubcon, it isn't treating it as anything really. Same as with Touka being abused by her workmates, this stuff is just being introduced then ignored by author until she remembers it, because the writing is incoherent mess saved only by art and few hot scenarios.
And I fully welcome "Californian brainrot" when it means teachers that give their students alcohol, let them sleep in the same room, and then sneak in their beds in the middle of the night are treated as rapists. In real life, any school were something like that would have happened and public learned about it, the teacher would get fired and prosecuted. Not just in California, in most first-world countries