Single-father household. The father hires a tutor, Rie-sensei, to help his son prepare for his exams. Rie-sensei is a married woman who runs a private tutoring school in the same town and has been helping the son since he was in elementary school. One day, the son asks Rie-sensei to show him her ass as a reward for improving his grades. Unable to refuse, she reluctantly agrees and shows him a glimpse of her tight, peachy buttocks, saying "It's our little secret." From there, a chain of forbidden pleasures begins...
