He is a guide through the labyrinth.

A great labyrinth spreading beneath the maze city of Remain. Even five hundred years after its discovery, the full extent of this labyrinth remains unknowable. Within it exists the profession of "guide." Yuri, a guide of exceptional skill, roams through the great labyrinth alongside Crathia, a demon god that dwells within a sword. Troublesome requests arrive one after another. And what is the true identity of the mystery that spreads in the depths of the great labyrinth, even deeper than the unknown sixth layer? Another noisy day in Remain begins today.