Nanako

A shy young girl who has lost her memory. She can fly, has super strength, and can become a giant. She stays with Yotsuya and Shibuya, as Yotsuya has promised to help her get her memory back. They give her a costume and call her "SuperGirl". However, she is unaware that they only want her to help them fight crime. She experiences some strange things as a hero, for example turning into a boy named Nanano. At one point her powers disappear. (Source: Wikipedia)