Koshigoe Maki

Ai's rival and a food-loving deliquent who goes by the name "Massacre Maki", she's said to be the evilest, worst existence in Shounan. She has run from her home and has no place to live in, the only thing she took with her is her large bike.

Spoiler

She has grown up in the same orphanage as Hiroshi and they were good friends when they were children. After Hiroshi was adopted by Hase family, he made a promise with Maki that they will meet again someday.