Nanako Momoi is a girl who appears small and cute until she opens her mouth. She is very impulsive and violent by nature, which cause many of her peers to be repelled by her and to fear her. 

After the incident at her house when Uehara attempts to save her from her grandfather's experiments, she switches bodies with Uehara. As a boy, Momoi in Uehara's body is much more popular for her/his confidence and athletic ability, especially with the female students. Despite the fact that Momoi threatens Uehara concerning what he can do with her body, she abuses his body in all sorts of ways (for example: masturbating, flirting with beautiful older girls, and even going to hotels with some of those girls and having sex with them). 

Unlike Uehara, Momoi enjoys being a guy and wishes to stay in her new body as long as possible. In the first volume, as a guy, she develops an attraction and feelings for her best friend Makoto Shiina, and the feelings are returned. The two eventually start dating.