Nana Chigusa (千草ナナ, Chigusa Nana) is a 17 year-old second year high school student in class 2-A of Sakuramizo Academy. Tall and beautiful, she is at the top her class and is admired by her peers, friend and most who know her. Nana is the vice-president of the student council, However she places herself under excessive stress trying to maintain her top grades, and meet her club and student council obligations. One of her teachers recommends that she take "breathers" to help relieve her stress.
That same day, the mother of her next-door neighbor and childhood friend Kaoru Sugimura, asks if she will hold on to a bag of "items" that she feels are distracting Kaoru from his studies. Nana agrees, and while stressing over how to take a "breather" to relieve her stress, she looks inside the bag. Inside she finds, among other items, a black leather bondage outfit. Although disturbed by the fact that her childhood friend has such things, and the outfit is apparently her size, she decides to try it on. Unfortunately, the straps that secure the outfit onto the wearer include a lock, which closes on her, and the bag does not contain the key.
Nana is therefore forced to go next door, with a long coat on, and ask Kaoru to help her get out of the outfit. Kaoru takes advantage of the situation to admire to view, forcing Nana to model the extremely embarrassing outfit in exchange for getting her out of it.
Although initially mortified by the experience, Nana finds that it in fact relieved her of the stress she had been under, and allowed her to perform far better in class than she has in a long time. This one encounter brings her to ask Kaoru to assist her with more "breathers" and thus begins an S&M relationship between the two.
Later in the story she is seen wearing an identical outfit with a cat mask.
Nana is smart, and when not taking a "Breather" normally a very modest woman in public. Around Kaoru though she can be a bit more seductive.
She is has been found to be highly submissive, and enjoys "Breathers" very much.
She has also been found to be determined and loyal to those she cherishes, and will go to any length to keep her bond with Kaoru, even to the point of exhibitionism.
Initially she wasn't fond of the relationship with Kaoru, but over time she has grown to love him and even tracked him down to confess her true feelings. As well as participate in exhibitionism. She seems very determined to keep her relationship with Kaoru alive but Kaoru is a complete fool.