The job of babysitting monsters... that's what "Mamoribito" is all about! The story is set in a world where a giant dragon appeared suddenly and swallowed the country along with the treasure inside it. People started to adventure inside the dragon's body to find the treasure, but some adventurers got stuck inside and couldn't return to the surface. One of them, Ariaris, was taken in by Lumon, who runs a 'daycare' business. She helps Lumon with his job taking care of the monsters' children... The story is a mix of Babysitting and Fantasy.