If I had to say, the one walking next to you is the Demon King.

In a world where magic breathes, in the age of stars and chanting……. The Baumaff family has served for generations as administrators of "Cocytus," a mutual network of monsters. The year is 1002 by the kingdom's calendar……. A brave hero who set out to defeat a non-existent Demon King is supported in both obvious and hidden ways by a boy from the Baumaff family and the monsters around him. However, she doesn't act quite as he intends……. This story is a grand tale of embarrassment woven by a certain boy and his cheerful monster companions, centered around a single girl……