Houko Byouinzaka

She is Yamane's elder sister and the professor's assistant, she is cold and heartless towards Iwai. She allowed herself to be Yamane's "Instead" as a way to relive her from the blood lust due to the pressure of killing goods that she possesses by allowing Yamane to inject her with a saline solution as a way to act out the latter's murderous intend. it is hinted that she has gotten so used to it, that she develops a kind of sexual arousal everytime Yamane does that sort of thing.

Just like any participants of the "Murderer's Game" both she and Yamane also desires the wish that comes with killing the "Hair Queen" who happens to be Iwai.

(Source: ANN)