Based on the erotic game by Black Lilith & Anime Lilith.

Asagi Igawa is a veteran Shinobu. After defeating an arch enemy a long time ago, she thought she could finally settle down. Yet, her arch enemy was revived from death through a pact made with the head demon in the city and swearing to take revenge on her by hurting those who are close to her. Her boyfriend, sister (a Shinobu) and her are part of the act being abused emotionally and... sexually...

(Source: Anime News Network)