they played a "game" where the first one to fall in love with someone loses. then they fell in love with each other but because he tried to deny his feelings he had violent sex with her to prove to himself that it's only about sex and when she gave an indication about developing feelings he made sure to let her know their relationship was only physical and then he fucked a bunch of other girls to convince himself he doesn't love her but now he is impotent if it isn't Sayo.

I know Kiriyama should suffer but can someone please remind me what he did? Thanks!