The main protagonist of the series, Masato starts out as a freshman living on his own in an apartment in Tokyo. He's a pretty laid back guy who loves pretty girls and Hawaiian shirts. Apparently, he is childhood friends with Yuki Nomura, having attended the same kindergarten together. Although he doesn't remember their friendship, he allows Yuki to live with him and call him "Maa-kun." His homeroom teacher, Mariko Mizutani, also eventually takes residence in his apartment as well, threatening to reveal to the principal that he and Yuki live together (she is unaware of Yuki's true gender).

He has a huge crush on the most popular girl in school, Kaoru Oozora, and starts dating her later in the series. Although he loves her very much, he is somewhat attracted to Yuki, despite him biologically being a boy. He comes up with a plan to date Kaoru in public, but secretly be Yuki's lover at home.