家族は（俺以外）サキュバスでした ～二人の姉と母との性活で精液を搾り取られます～

"Ta-dah♪ Sakura-chan, Kaede-chan. Congratulations♪ You have now awakened as a splendid succubus."

Sakuba Takuya (the protagonist's name is changeable) is in a family of four, consisting of his mother Yuri, and his twin sisters, Sakura and Kaede. Even though he is not blood-related to them, he spends his day with them like a real family.

One day, his sisters forget about themselves, crave for him and attack him. Yuri, witnessing the scene, happily announces that she is a succubus while Sakura and Kaede are partial succubi. As is the nature of succubi, they need to ingest themselves with semen regularly.