Kazoku wa (Ore Igai) Succubus Deshita ~Futari no Ane to Haha to no Seikatsu de Seieki o Shiboritoraremasu~

"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.

"When your sisters are in a lewd mood, I want you to comfort them."
"Specifically, it doesn't matter if it's their mouths at the top or at the bottom, just let them have lots and lots of your semen."

Accepting Yuri's proposal, with his succubi sisters, Takuya's sex life begins.

[Translated and edited from the official website]