To LOVE-Ru

Synopsis

A childhood friend of Lala, Ren Elsie Jewelria, arrives on Earth claiming he is the only one manly enough to marry Lala. He constantly attempts to impress Lala by showing off his strength, speed, and looks, but all his efforts are in vain. After failing many times, Ren asks Rito how he is able to be manly enough for Lala, and in the process is hit from behind by a frisbee and accidentally kisses Rito. Ren watches Pocky (a spoof on Rocky), an inspirational story of how to be a man, and he works out non-stop in order to get Lala to love him. Eventually, Ren completes a 120-kilometer marathon and goes to Lala to hear her finally tell him how manly he is. However, at the moment Lala is confessing his manliness, he sneezes, causing him to turn into Run, a girl. Apparently, whenever Ren sneezes, his body and mind change genders into the innocent Run, and vice versa, an inherent ability of his species.

(Source: Wikipedia)