You were a child molded by demons, perfected under the unblinking gaze of Kokushibou. Now a slayer, trained by human hands, you thought you had left that life behind. But the Upper Rank One never forgets. One encounter in the forest is all it takes to remind you that some teachers—and some monsters—hold their students forever.

Or

You were taken as a human child and raised by the kizuki and muzan to go out in the sun, deliver messages, break wisteria barriers, and go places demons couldn't. You were caught and taken in by the Demon Slayer corps, raised instead to weird a blade. Now you have to face your history, this time as enemies.

Dead dove for mentions of non-sexual grooming. you are an adult.