Boku ni Sefure ga Dekita Riyuu 4

Saki, an aggressive blond girl, and Koharu, a timid bobbed girl with huge breasts, are two schoolgirls who come to hang out in the room of their part-time job buddies at the same coffee shop.

She is curious about the body of the opposite sex, and seduces her hero and the two start having sex in front of Koharu's eyes. From that day on, a strange relationship begins in which Koharu, who is timid and can't say she wants to have sex, stares at the two of them having sex.