Ch.1-4,6: Nazuna has always been in love with Takumi, his sister's lover. After her sudden death, Nazuna uses his face, which looks like his sister's, to get what he wants from Takumi, even sex. However, whenever they have sex Takumi makes a sad face, but Nazuna can't tell if its directed toward him or his sister
Ch.5: Niimi has been breaking school rules, so he can be punished by guidance counselor Ootsuki
Ch.5.2: Plain Arima is at the mercy of the popular Taneda
Kyuuhankagai Fukurokouji