There's a Demon Lord on the Floor manga volume 4 features story by Hato and art by Masaki Kawakami.

The Phantom Waitress

Ghost-girl Nukadoko is jobless and short on money. Good thing she lives in a restaurant! Can she make it as a server despite the fact that the customers can’t see her? Meanwhile, other staff members are losing cash while playing an addictive smartphone game, Kouichi’s raising a baby dragon, and Amon wants to head to the beach to meet the Devil of the Deep. It’s time for a fourth helping of this hellishly delicious comedy!