Aiko Nanase

About

Don't let Aiko's size or child-like face fool you: she's Rena Nanase's older sister (who possibly suffers from dwarfism), and just as sex-obsessed and strong-willed as Rena, much to Rena's consternation. She has sex with Hasegawa, who was fooled, like many before him, into her child-like act (due to her child-like body, she pretends to be younger than she really is to hook up with older men; she is nearly accosted for that at the beginning of her chapter).

In the visual novel, after she's reprimanded by her own younger sister, she again has sex with Hasegawa, but before she continues, she's yanked away by Rena, much to Hasegawa's surprise. In the manga proper, she, having dropped her child-like act, has sex with Hasegawa's younger brother, Kasuki, when Kasuki was hanging out with Noriko Kamata, with whom he had started a slight relationship with; given that Kamata is still with Hasegawa, it's implied that Aiko and Kazuki start a relationship.