Koshimizu Sachiko♀

Sachiko is a playful young girl with astounding confidence, priding herself in being the cutest. She denies all her failures and even while falling down an airplane she will try to keep a confident face. She's kind of a sadist, getting a kick out of showing other people how superior she is to them. Her reasons are very self-centered however: she doesn't want people to suffer for no reason or at the hands of others, just suffer because she is better at the task and they become aware of it.

Sachiko has been shown to be a 4.0 GPA student and will help other idols with their school work without asking anything in return. Additionally, she works hard and is said to have a willpower of steel. She's also very friendly with younger idols. All in all, while Sachiko has a ridiculous ego, she doesn't intentionally want permanent harm on others.

[From Project IM@S Wiki]