Koto is a demon girl from the demon plane who serves as the initial referee and commentator for the Dark Tournament, the illegal martial arts competition that forms the core of the second major story arc. She appears as a fox-like or cat-like demon with distinctive ears and a tail, and she takes her role as an official very seriously, memorizing the entire tournament rulebook. In the early rounds, she is positioned in the ring to call matches and enforce rules, and she is notably cheerful and openly enthusiastic about the violence and suffering of the fighters, often expressing delight at the pain and cracking of bones. However, her enjoyment of brutality is later clarified: she only finds such violence acceptable when both contestants are capable of fighting back fairly. This moral nuance is demonstrated when she interrupts a match between Kurama and Bakken by beginning a ten-count, attempting to stop Bakken from beating an incapacitated Kurama, showing that she is not purely sadistic.

Koto’s tenure as referee ends when she protests the tournament committee’s underhanded manipulation—specifically, a double-fault decision made against Yusuke Urameshi during his match with Jin. The committee claims she counted too slowly, and she is replaced by Juri, moving to a commentator role in her own booth for the remainder of the tournament. Despite this demotion, she continues to provide lively commentary and eventually helps Juri escape the collapsing stadium, risking her own safety for live coverage. She later returns as the announcer for the Makai Tournament (the Demon World Tournament) held by Yusuke in the demon plane, cementing her role as a recurring figure in high-stakes demon fighting events.

Personality-wise, Koto is energetic, confident, and shrewd. She often puts on a cute and cheerful facade, but she is quick-witted and not above making pointed remarks, such as jabbing at Juri for being a former cocktail waitress. She is ambitious and takes great pride in her work as an announcer and entertainer, becoming something of a pop idol in both the human and demon worlds. Her motivations appear to center on her love for her job and her desire to be seen as a professional, though she also has a clear sense of fairness—she respects the rules of the tournament and objects when those rules are bent by corrupt officials.

In terms of relationships, Koto harbors a known crush on Kurama’s demon form, Yoko, though this is never reciprocated. She briefly becomes the object of affection for the fighter Chu, but she does not share his feelings. She has a rivalry-turned-friendship with Juri, and she interacts frequently with the tournament staff and fighters, but her most notable dynamic is with the audience and the fighters themselves, whom she treats as both performers and subjects of her commentary. She does not possess any notable combat abilities; her role is purely that of an announcer and referee, though she demonstrates nimble acrobatics to navigate the arena.

Over the course of the series, Koto shows some development from a gleeful observer of violence to someone who actively steps in when a match becomes one-sided and unfair. She also becomes more integrated into the demon world’s entertainment scene, eventually forming a demonic idol trio with Juri and another character after the events of the main story. Her background as a demon of the fox or cat variety ties her to the demon plane’s diverse species, but she remains a supporting character who never wields supernatural powers or engages in combat herself. Her primary abilities are her knowledge of tournament rules, her energetic presence, and her acrobatic agility.