Arimi went out with Yuu for three months while they were in junior high. Since it was a three month deal, they broke up right afterwards. But Arimi couldn't forget about Yuu and still loved him. Arimi was a very popular girl and had many boys after her, but she only wanted Yuu.
After meeting Yuu again and finding out about Miki, she teamed up with Ginta to try to pull Miki away from Yuu.