"TOKKO" is a 13-episode anime series that blends supernatural horror, action, and mystery. The story centers on Ranmaru Shindo, a young man who joins the Special Mobile Investigation Unit, also known as TOKKO, after surviving a brutal massacre at his apartment complex. The incident, which claimed the lives of his family and friends, is linked to a mysterious box discovered during a construction project. This box unleashes demonic entities called "Phantoms," which are responsible for the carnage.

Ranmaru's investigation into the massacre leads him to uncover a deeper conspiracy involving the Japanese government, ancient artifacts, and a secret organization known as the First District. The First District is tasked with combating the Phantoms, which are revealed to be manifestations of human desires and sins. Ranmaru discovers that he and his sister, Saya, possess unique abilities tied to the Phantoms, making them key figures in the ongoing battle.

As Ranmaru delves further into the mystery, he encounters other members of TOKKO, including the stoic and skilled Shizune Rokujo, who becomes a mentor figure, and the enigmatic Daigo Tokiwa, whose motives remain unclear. The series explores themes of vengeance, justice, and the blurred line between humanity and monstrosity as Ranmaru confronts both external threats and his own inner demons.

The narrative is driven by intense action sequences, supernatural encounters, and a gradual unraveling of the truth behind the Phantoms and their connection to the First District. The series maintains a dark and suspenseful tone, with graphic violence and mature themes that underscore the stakes of the conflict. By the conclusion, Ranmaru's journey comes full circle as he confronts the source of the Phantoms and grapples with the consequences of his choices.