Sakaido doesn't just solve murders, he walks through the killer's mind while it's still thinking, watching a murder happen from inside the person committing it. The show builds toward a twist that recontextualizes everything you've watched, revealing that the real investigation was always about Sakaido himself. This is a serial killer procedural that becomes a tragedy about a man so damaged by his work that he can't tell anymore where the job ends and his own fractures begin.

Sakaido is a gifted former detective who now works with Kura, a specialized police squad that solves crimes with the Mizuhanome system. Using traces left at a crime scene, the system turns a culprit's unconscious mind into a strange virtual world called an id well, and Sakaido enters it to uncover who the killer is. Only someone who has taken a life can make the dive, and Sakaido qualifies: after his daughter was killed, he took revenge and is now behind bars, helping investigators from confinement. Behind a string of brutal, baffling cases hides a figure known as John Walker, who creates serial killers, and what look like separate murders point to something darker, including clues tied to his daughter's death. The genres mark it as a psychological sci-fi mystery thriller for viewers who like a dark puzzle.