Saya Akabane

She's Aya's elder sister, who has a sweet and gentle outlook, but actually she's a sadistic and a feared delinquent who partners up with the equally sadistic bosozuko school nurse, Oku Kaname. There is a running gag where Saya cares more for Oku than her younger sister Aya, in fact both she and Oku would even pick on her, thus making Aya fearful whenever the two are around. It is also suggested that both she and Oku are in a relationship.