Four hundred years ago, a massive prison break from hell sent countless vengeful spirits known as Dead Souls flooding into the living world. These entities survive by preying on the living, possessing humans and feeding on their life force. To combat this threat, King Enma, the ruler of hell, appointed the Kagarite family as Hell Wardens, forcing them to hunt down and return these fugitive spirits for generations. The story follows Higuma Kagarite, a seemingly carefree and gentle 16-year-old high school student who carries this heavy burden. While he appears laid back, smiling and spending his free time playing video games, he transforms during combat into a grim and merciless executioner who shows no mercy to the monsters he pursues.

The plot kicks into motion when Higuma encounters Ayaha Kuromine, a strong-willed and正义感十足 18-year-old girl who has recently developed a troubling habit of stealing things for no reason. After Ayaha stands up for him against a drunkard on a bus, Higuma reveals his ability to see the demon possessing her, forcing her into this petty theft. He exorcises the spirit, but the trouble is only beginning. Upon returning home, Ayaha discovers that her once-kind older brother has become an abusive tyrant, terrorizing their parents and household. She correctly deduces that another Dead Soul has possessed him. Higuma arrives just in time to save her, exorcising her brother and revealing his true identity as a Hell Warden. Intrigued and indebted to Higuma, Ayaha begins assisting him, eventually receiving her own powers from King Enma as a Bunreisha.

The narrative delves deep into the tragic history of the Kagarite family. They are not just fighting a random assortment of demons; they are locked in a generations-long blood feud with a particularly powerful Dead Soul named Shakunetsu Akagane, who has a 879-year sentence. For reasons rooted in the past, Akagane has made it his mission to systematically destroy the Kagarite clan. Every ten years, he appears to murder the current head of the family. Six years before the main story, Higuma watched helplessly as Akagane killed his stern father, Azuma, and his aunt, Haruma, right in front of him. This traumatic event is the source of Higumas deep-seated pain and explains why he forces himself to become a cold-blooded warrior during battle, despite hating violence and the duty he is forced to perform. He dislikes the job so much that he has trained himself to switch off his emotions entirely to ignore the pleas of the spirits he is destroying.

As the series progresses, Higuma and Ayaha are joined by other allies as they track down Dead Souls across the city. They face a variety of demons from Japanese folklore, each with unique abilities and tragic, desperate motivations for trying to extend their stay in the living world. A major arc involves the investigation into Akaganes whereabouts, forcing Higuma to confront his past trauma and the seemingly inescapable curse of his family, which is also bound by a pact with the often-inscrutable King Enma. The young boy who serves as the avatar for the king operates purely on his own whims, adding an element of unpredictability to the heroes mission. Through each battle, Higuma struggles with his identity, trying to reconcile his gentle nature with the violent, monster-hunting legacy he cannot escape.