One late night, on his way home from the station to his apartment, the protagonist hears the sound of a girl crying under a bridge.

Although the area isn’t particularly unsafe, it’s certainly not a place where a girl should be alone at such an hour. Unable to ignore it, the protagonist makes his way beneath the bridge. There, he finds a succubus curled up inside a cardboard box, hugging her knees. Through her tears, she begs him to let her perform an energy drain.

The protagonist reaches out his hand and says,
“If you're okay with it being me, I’ll help you however I can.”

And so, their life together begins.

[Edited from Steam]