Tenshi na Konamaiki

A girl named Megumi-chan has a hidden history. Originally male, she encountered someone claiming to be a magic user, who gave her a book containing a genie that grants one wish when blood is applied. She wished to be a man in a man's body, but the genie reversed her wish, turning nine-year-old Megumi-kun into Megumi-chan. As she enters high school, she confronts and defeats the school bully, who then develops feelings for her. Megumi continues searching for the book in hopes of undoing the transformation.