千住 静

She is the childhood friend of the Senoo siblings. She is younger than Kazumi.

We learn in her dark route than she know everything about the sex life of Tsugumi, she likes heard Tsugumi's stories for her masturbation session. She even peeped at her having sex. 

She's apparently into SM, her as the Sadist.

She is secretly in love since her childhood days of the protagonist but is too shy for saying it to him.
/