Nana to Kaoru (2011)

Original title: ナナとカオル

Kaoru is a 17-year-old boy with an SM fetish, secretly dreaming of an SM relationship with his childhood friend Nana. One day Kaoru's mother asks Nana to hide all his SM toys so that he will study for a change. However, Nana finds the leather one-piece that Kaoru bought and tries it on, but she accidentally locks it and does not have the key! This is the beginning of a very strange relationship..