Casper is a daemon who appears in the first episode of the series. His physical form is described as being large and jellyfish-like, featuring a single eye. His most notable ability is turning himself and anything he touches completely invisible. This power is versatile and can be applied on a massive scale, as he is capable of rendering entire buildings and other large obstacles unseen, leaving targets with nowhere to hide. He can also selectively turn parts of an object or being invisible, using this ability for psychological torment.

At the outset of the story, Casper is owned and controlled by a bounty hunter named Iori Kusanagi. Their relationship is one of forced servitude, as Iori uses a shock collar to keep Casper submissive and enforce his commands. Casper functions as a tool for his master, used to hunt down the young protagonist Kento and his daemon Anna. He is instrumental in Iori’s aggressive and dangerous pursuit, which shows no regard for the safety of a child.

The dynamic of this relationship changes when Kento, after a violent confrontation, removes the shock collar from Casper. Without the collar compelling his obedience, Casper’s role in the narrative shifts immediately. He turns against his former master, killing and devouring Iori as a direct act of retribution for the years of control and abuse. Following this event, Casper is freed from his enslavement, marking the end of his direct involvement in the story as presented in available information. No further details regarding his background, personality, or subsequent development are present.