Despite being 17 years old, Kaoru is still a virgin and has a fetish for S&M. His childhood friend Nana, who is admired by boys for her perfection, has always been the object of Kaoru's SM fantasies. However, their friendship has slowly weakened over time due to their different social circles and Kaoru's lack of interest in academics. One day, Kaoru's mother entrusts Nana with some of her son's S&M toys for safekeeping. Curious, Nana puts on the leather one-piece that Kaoru had acquired, but is then unable to take it off without the key! After finally freeing Nana from the constrains of the one-piece, she discovers that she is intrigued by Kaoru's fetish more than she initially thought. This curiosity leads to the two engaging in "breathers" to help Nana relieve the stress she feels while trying to maintain her flawless academic record and reputation.