Kouta is a young soldier who perished in battle within the Land of the Living. After death, he awakens inside the mouth of a colossal dragon, a bizarre interdimensional space existing between life and death. Initially confused and disoriented by his state and surroundings, Kouta encounters Nono, a young dentist dedicated to maintaining the dragon's teeth.

Despite his fear and unfamiliarity, Kouta adapts to this strange reality. He forms a connection with Nono, drawn to her kindness and commitment to her duty. Through her, he learns about the dragon dentists' vital role and the threat posed by the Bell-nose, destructive entities invading the dragon's body to induce catastrophic decay.

When the Bell-nose launch a major assault, Kouta instinctively joins the dragon dentists in defense. Witnessing Nono's resolve and understanding the dire threat to the dragon, Kouta makes a critical choice. Recognizing his nature as a departed soul, he realizes he possesses a unique ability to interact with the Bell-nose core, inaccessible to the living.

Kouta deliberately allows the Bell-nose core to possess him. This self-sacrifice enables him to contain the destructive entity within his own spiritual form. Containing the core prevents immediate disaster but condemns Kouta to be dragged into the void alongside it, undergoing a second death to save both the dragon and Nono.

In his final moments, Kouta expresses no regret. He reassures Nono, accepting his fate with peace and contentment, knowing his actions protected her and served a vital purpose. Kouta's presence, though brief, profoundly impacts Nono and fulfills a crucial role in preserving the dragon's existence.