Haruka Kousaka

Yuumi Rin obsessed fan, Haruka is the one who had been bulling Ai since she couldn't help to introduce her with him even if her mother was working with him. However with a little help of Jun-pon, Haruka becomes near to Ai. Source: Chapter 3

NoHeart Note: Maybe she will be Ai's best friend... but wait till further in story to confirm this.