Kyonyuu Daikazoku Saimin follows Mamiya Yuuichi, who wields a penlight with powerful hypnotic abilities to manipulate his foster mother and stepsisters, using them as outlets for his sexual desires. As the scandalous behavior in the Mamiya household becomes known, concerned neighbors visit, only to fall under Yuuichi’s hypnotic control, escalating the chaos and forcing him to take drastic measures to handle the spreading rumors and interference.