First-time sex with a classmate at a manga cafe while keeping their voices down!
Aihara-kun (protagonist) was masturbating in a manga cafe booth when a girl in his class named Hirasaki-san (heroine) saw him at the exact moment he was ejaculating. To make up for his embarrassment, she decides to let him watch her masturbate. However, just seeing her masturbating wasn't enough for him to settle down...
(Source: DLsite, translated)