Nana to Kaoru is an adult manga aimed at a specific kind of audience. The atmosphere of the manga is highly lustful and charged and features a 17 year old boy who has an S and M fetish which he wishes to pursue with his childhood friend, the beautiful Nana who has impeccable grades and a personality and body that makes everyone who meets her go instantly crazy for her.
They have drifted apart a bit because of Kaoru’s failing grades in Nana to Kaoru Manga. One day however, Kaoru’s mother gives Nana some of his toys for safekeeping and Nana ends up putting a piece on which she barely is able to get out off.
However in Reading Nana to Kaoru, over this experience she realizes that she actually likes Kaoru’s fetish more than she lets on. Over time she and Kaoru develop a few breathing exercises, that involve parts of his fetish to help her relax more.