Yakumo Saitou is a college student born with a red left eye that grants him the ability to see ghosts and spirits. He believes that every spirit lingering in the human world is tied to an unresolved cause, and that by identifying and resolving that cause he can help the spirit move on to the afterlife. He keeps his power largely to himself and leads a withdrawn, cynical existence until Haruka Ozawa, a fellow student, comes to him in desperation. Her friend has become possessed by a ghost after a drunken dare in an abandoned building on campus, and she needs Yakumo’s help.

Haruka initially doubts Yakumo’s abilities, but he proves his power by revealing a private detail about her deceased younger sister. Reluctantly, he agrees to assist, and together they uncover the truth behind the possession—a murder linked to the building’s past. This first case, detailed in the opening volume The Red Eye Knows, sets the pattern for the series: a supernatural incident rooted in human emotion, crime, or trauma, investigated through a blend of psychic perception and logical deduction.

The setting is contemporary Japan, mostly around the university and its surrounding urban areas, though cases later expand to a women’s university, rural locations, and sites tied to Yakumo’s own dark family history. The narrative tone blends mystery, psychological drama, and horror, with occasional romantic undertones in the growing bond between Yakumo and Haruka.

Supporting characters include Detective Gotou of the local police, who knows Yakumo from childhood and often calls on him for help; the frightened but well-meaning detective Ishii, who admires Gotou; and other recurring figures from Yakumo’s past, including his troubled mother Azusa. As the series progresses, Yakumo’s own origins become a central arc. Volume 6, To the Limits of Despair, is a two-part prequel that explores Yakumo’s childhood and the traumatic incident that scarred him, while later volumes like The Spirit of Salvation and The Guidepost of the Spirit deepen the mysteries surrounding his red eye and the forces that seek to control or destroy him.

The main series spans twelve volumes, concluding with The Depths of the Soul. Alongside the core story, there are several side story collections (Secret Files and Another Files) that offer extra cases and character moments, and a prequel spin-off series titled Ukikumo Shinrei Kitan, set in an earlier era and focusing on a different protagonist. Throughout, the series balances standalone supernatural mysteries with a long‑running narrative about grief, connection, and the weight of the past, all anchored by Yakumo’s reluctant heroism and Haruka’s determined humanity.