Manga Kanojo ni Naru Hi
Becoming a Girl One Day
Genre: Drama , Sci fi , Romance , Shoujo , Gender Bender
Miyoshi is always competing and losing against his childhood friend, Mamiya, who is good at everything. One day, Mamiya collapses from illness and is hospitalized for several weeks. When he returns to school, it turns out he is genetically female, and has decided to try living his life as a girl now much to Miyoshi's horror.