Megumi Amatsuka used to believe she was a boy until encountering someone she thought was a magician. This individual gave her a mystical book, from which a genie would emerge to grant one wish when blood was applied to it. Megumi wished to be manly, but the genie granted the wish by transforming her into a girl instead. Years passed, and Megumi entered high school where she immediately confronted the school bully, who naturally fell in love with her. She began searching for that magical book again, hoping to reverse the spell cast upon her.
Though physically an attractive female, Megumi retained her masculine mannerisms and fighting prowess, leading to the formation of the 'Megu-chan Protection Club,' a group of misfit admirers. Megumi is fiercely protective of Miki, and there are hints she might have a crush on her, though this remains ambiguous.
(Source: Wikipedia)
It was later revealed that Megumi had never actually been a boy. The genie merely altered her memory to make her believe she had once been male. Her original wish was to become a boy after Genzo saved her from falling glass.
