Ore to Atashi no Kareshi-sama

Hayato and Chouko are twins who are as unlike each other as night and day. Chouko is a shallow princess who's main concern is her own looks and cute things, while Hayato is the cool but overpotective brother with a penchant for sabotaging any potential relationships for Chouko. So it's only natural that he would do the same when Chouko confesses to the school prince, Tsukiyono (albeit, mainly for his looks), and finds herself with a date. Things become very, very complicated, however, after an argument over Chouko's love life ends up with them both tumbling down the stairs. Bizarrely, they both find they've switched bodies, with Hayato in Chouko's body and Chouko in Hayatos. Whats worse, and much to Chouko's horror, Tsukiyono starts to fall for Hayato in Chouko's body even without knowing who he is.