Shouwaru Iinchou♂ wo M-jou-ka Choukyou

Naruse, a timid young man, is being bullied by his classmates. Naruse asks the class president for help, but the class president ends up begging Naruse for money as well. Naruse uses black magic on the class president to turn him into a girl. The class president is sexually trained by Naruse and other classmates. Gradually, SHE becomes a masochistic girl in body and mind...
(Source: Fakku)