Pied Piper (an owari no seraph detective au)

When children around the small city of Sanguinem start disappearing, the Progenitor Detective Agency's on the scene.
A rookie detective, Mikaela Hyakuya has been on this case for weeks now, coming up with dead end after dead end.
In a stressed tizzy, he finds himself at a back alley bar where he meets a charasmatic bartender who seems far too eager to help.