When a city boy, Kinuta Jun, transfers to a school out in the country side, an older girl starts following him around. This is Mizobuchi Chinana-senpai, a self-proclaimed slut who wears a revealing school uniform and doesn't shy away from dirty jokes. However, sempai is a fake slut, whose lack of knowledge and experience is plain to see.

Humans and demihumans live together in peace, and in this world, there's a normal human named Hironori Tabata.
One day, an angel named Suzuki Lina went out to find him and said she wants to have sex with him...the reason—? The Demon King will be resurrected in the future and Tabata's son will be the hero that will fight and defeat him.

Kusaka is an older man who loves marshmallows, and Wakabayashi is an OL (office lady) who loves Kusaka. Their relationship unfolds at their office.