Hinata Sugai

Represents the Naraka Realm (Hell Realm), has a little fire-spitting-demon pet by her side at all times that converts to a full sized demon when Hinata can't suppress her Naraka bosatsu. Later in the series, when Ikkou is on the verge of awakening she often commands her demon to burn him, often successfully preventing him from awakening while others times it seems for the hell of it. She is Sakura's younger sister. She appears very calm and rarely speaks. Her hobby is collecting and studying haniwa, and there is an episode in the second season devoted to the Haniwa Research Club which she joins - the school's smallest club.

[Wikipedia]