Miyano Amata, known as the "Perfect Prince" for his intelligence, looks, and cool personality, is asked to substitute for his sister as an attendant at a doujinshi convention disguised as a loligothic girl. There he meets a girl from his class and they become friends, but he must crossdress in order to be with the girl while learning about the fujoshi fandom.
(fudanshi = BL fanboys. Some may be gay, but most are straight. More info can be found here.
fujoshi = (literally: rotten girl) a pejorative Japanese term for female fans of manga and novels that feature romantic relationships between men, often with the implication of Yaoi concept.)