Sera, Vagia, Anus, and Delich are Succubuses who came from the Demon Realm, To maintain their lifeform Succubus have to sex with humans which would draining their lifeforces. As result, they keep attacked and pursued by the demon exterminator.

As they tired of keep pursued by them. They decide to making contract with humans to do sex instead for them. Their preferable human to contract with are the younger one with strong inner sexual desire.

As they searched, they found exactly 4 human candidates for them to contract with: The protagonist, Ai Mizushima, Hikari Shibusawa, and Kaede Tachibana. The certain incident makes the succubus and the humans agreed to contract with each other.

How their each other fate be unfold on this story would up to the player to decide…….