Ryūsuke Tagawa, a junior high school student from Tokyo, travels to Tokushima during summer vacation to visit his teenage cousin, Tomomi Sato. While playing near the Anabuki River, both are swept away by a strong current and drown. A dragon intervenes, rescuing them and delivering them to a mysterious old man. This figure informs Ryūsuke and Tomomi they have died but offers them a chance to return to life if they journey through the spirit world to discover their life's purpose.

Initially perplexed, Ryūsuke agrees to undertake the journey with Tomomi. Their exploration begins in a gloomy town reminiscent of the 1960s, where they immediately face terrifying ordeals: violent rogues engaged in mutual killing, doctors mutilating patients, and cycles of death and resurrection. These encounters reveal they traverse hellish realms. Ryūsuke endures extreme psychological and physical trials, including disturbing visions of a surreal "modern hell" filled with graphic violence and bloody imagery.

Throughout this odyssey, Ryūsuke confronts themes of mortality, spiritual reckoning, and the search for meaning. The relentless challenges test his resilience, forcing him to grapple with profound questions about existence. Navigating fear, moral ambiguity, and the weight of his mission within increasingly intense and otherworldly landscapes catalyzes his personal growth. This quest through the spirit world shapes his understanding of responsibility and self.