Doi is a male classmate of Shuichi. In middle school, Doi would often times bully Shuichi for his feminine appearance. But in high school, Doi begins to take an interest in Shuichi when Doi sees them with an older woman and wants to know how Shuichi knows her. Doi learns that Shuichi is a transgender teen who wishes to transition to a girl, and that Yuki is a transgender woman who has already transitioned to a female. This sparks an interest when he sees Shuichi dressed in a girls' uniform, prompting Doi to convince them into wearing it to school. Shuichi does so, but with less than desirable results. Later, Doi begins to consider cross-dressing as a teenage girl himself. Doi is not a transgender person, but seems to have a fascination with gender concerns and dressing as the opposite sex.
Doi begins attending the same all-boys high school as Makoto and Shuichi, while Yoshino and Saori begin attending another high school where school uniforms are not required. In middle school, Doi used to bully Shuichi in the most cruel and demeaning way because of Shuichi's feminine appearance and demeanor. But when the two attend high school, Doi tries to befriend Shuichi and tells them that he is sorry for the bullying when they were younger. However, Shuichi takes the opportunity to 'tell off and take down' Doi, later expressing wonderment that that was even possible to confront Doi in such a fashion. After graduating from high school, Shuichi moves out and goes to the same college as Doi. Shuichi continues to write a novel, which is given the title The Boy Who's a Girl (ぼくは、おんなのこ Boku wa, Onna no Ko).