A demon addicted to mysteries the way a serial killer is addicted to crime scenes. Neuro doesn't solve cases to help people, he solves them because unsolved puzzles physically hurt him. That single twisted rule generates every laugh, every twist, and every moment of genuine darkness the show has, turning a procedural into something that feels actively dangerous. Yako starts as his cover story. She ends as the only person who knows what he actually is, which means watching her realize she's partnered with something that could destroy her at any moment. The mystery format keeps you guessing at case solutions that are often obvious, but that's not the point, you're watching a demon learn what guilt looks like through a human who won't leave him alone.

Neuro is a demon with an insatiable appetite, but not for food. He feeds on mysteries, and having already solved every riddle in the demon world, he comes to the human world in search of the ultimate one. The problem: a demon must not let humans notice him, so Neuro strikes a deal with Yako Katsuragi, a high school girl whose father was murdered. He promises to help her find the truth behind that death, and in return she poses as the detective while he quietly cracks the cases. Their agency makes Yako famous as a teenage sleuth who never fails, but the real draw for Neuro is the negative energy people give off when they commit crimes, which he consumes as sustenance. Blending comedy, mystery and the supernatural, the story has the unlikely pair solving case after case to keep his hunger fed.