yuuto, a part-timer who is semi-cohabiting with his girlfriend, doesn't understand women's hearts and only fights with his girlfriend... he was consulting with "sui," a senior at his part-time job, about his love life. sui, who was listening to that, seduces yuuto, gets him drunk, and ends up having sex with him. since then, the two of them repeat erotic things during their part-time jobs. however, yuuto felt guilty towards his girlfriend.