Stormy Weather Comes to School! Growing Up With Miss Hinako

Gakuen ni Fuku Arashi! Adult Change Hinako-sensei (学園に吹く嵐！アダルトチェンジひな子先生) is the fourth OVA of Ranma ½ anime.

Hinako Ninomiya, Furinkan High's new homeroom teacher, is able to absorb battle aura from delinquent students like Kuno and Ranma and grow into a twenty-something version of herself. Of course, Ranma wants to learn her secret, but when Happosai reveals that Ranma would never be able to execute it, Ranma takes it upon himself to strike Hinako's pressure points (some of which happen to be very near her breasts) and stop her from draining the students. Hinako winds up draining almost the entire school in her battle with Ranma before he manages to strike her pressure points. Of course Happosai never told him he would have to repeat this almost every day for a month to permanently stop her. This story was originally featured in volume 25 of the manga.

Trivia

 * This episode introduces Hinako Ninomiya to the anime series