Ryûta Amazume

Kaoru is a 17-year-old virgin who has an SM fetish. He secretly dreams about an SM relationship with his childhood friend Nana. One day Kaoru's mom asks Nana to hide all his SM toys so he'll study for a change. However, Nana finds the leather one-piece that Kaoru bought and tries it on, but she accidentally locks it and doesn't have the key! The beginning of super strange relationship.

Nana, a model student who serves as student council vice-president, and run-of-the-mill virginal high schooler Kaoru are childhood friends. They embark on regular S&M play dates in secret as a stress release for Nana. For spring break, Nana goes on a school trip to a power spot in Nagano planned by the student council. Kaoru joins her, and a change occurs in their feelings.