Desperate to lose his virginity, student Morita Takashi follows an online ritual to summon a succubus after seventy-two days of abstinence. He is stunned when the summoned demon, Erilyn, bears a striking resemblance to his stepmother. As Takashi navigates his confusion and lust, he discovers a scandalous secret: his devoted stepmother is actually a succubus, leading to a forbidden and erotic relationship.
Struggling with his grades due to his distractions with Erilyn, Takashi is subjected to a "home tutor" roleplay that only further hinders his studies. After a chance encounter at a pool resort, Takashi discovers the shocking truth that Erilyn and his mother are the same person. Following a heated confrontation, his mother accepts him as her master, forever changing their relationship.