Claire is trying to sacrifice her dignity in order for them to join the group and calling out Sayaka for what she is doing a rape, escaping the "NTR" because she doesn't want to betray Shuichi.
Meanwhile Shuichi agree to have any girl enter him without much resistance, he is basically a "slut", it's the third girl who makes a sexual act on him and doesn't look at it as indecent although for a brief moment noticing something is off.
Seeing how Ikeuchi likes Chihiro, he gonna betray them so hard and it's all Shuichi fault. Probably unfortunately it will cost him his life, as Sayaka did the hair neck thing with him also... Shuichi is incompetent asshole.