It is group rape. Any sex without freely given consent is rape. Technically, it is not a foursome since Karino only holds Asuza during the "train", but Asuza clearly says Atsumu has nothing to do with this and does not want to have sex with Atsumu. so does Atsumu. Atsumu was forced to have sex with Asuza even though neither one wanted it, and Kuze raped too, because Atsumu did not want it at that time even from Kuze.
Nothing in this manga is "just there". You can discuss various aspects of the group rape or what you think of it, but it is what it is: group rape. And if rape is "just there", then what does that say about the story or the way we look at things?
That school is horrible .
Chill tf out oml
But that forced foursome was beautiful sh sh