Senoo Tsugumi

It reveals in her dark route that she lost her virginity one or two years ago and enjoy even her first experience with Ijiri-Kun ( one of her club member ) who didn't hurt, and then she start dating him.
After he cheating on her, she left him ( despite doing the same thing with other boys ). She is a sex addict, had severals partners ( 4 differents minimum ) and a lot of sex intercourses with her classmates, senpais and kouhais ( a single partner or severals at the same times ). She graduates from middle school 6 or 7 months ago and haven't had sex since.

She maybe have a brother complex, not sure because she show this side of her personnality after being infected.

She is a closet pervert, during her sexual intercourse with the protagonist, she tells him all what she experienced before, with details.

Despite being very experienced, she always had safe sex ( with condoms or with outside ejaculation ).