From MangaUpdates:

Saiki Takaya, a guy who is easily misunderstood, one day finds a flask containing the succubus Lilim. She is very attractive but, she also has the tendency to drain the life force out of people. She surprises the life out of him (literally) when she kisses him unconscious. The girl, Lilim, turns out to be a succubus who gains energy by kissing guys. Lilim then flies off for more "food," but returns later, saying that Takaya's life-energy was the "tastiest." From then, Lilim is accepted by Takaya's parents as a live-in girlfriend of sorts, and Takaya's heart seems to start wavering towards this voluptuous devil.