Tenshi na Konamaiki

A nine-year-old boy named Megumi Amatsuka dreams of becoming the toughest man possible. After rescuing a sorcerer from local bullies, he is given a magical book and uses it to summon a genie to grant a wish. Unfortunately, the genie is malevolent, and instead of becoming the manliest man, Megumi is transformed into the womanliest woman. Six years later, Megumi is a highly attractive girl at school, but beneath her feminine exterior remains the same assertive and tough personality he had as a boy.