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 the human world is an all-you-can-eat buffet of unsolved crimes and hidden secrets. The problem: demons can't walk around openly without causing a supernatural incident, so Neuro strikes a deal with Yako, a high school girl desperate to uncover a mystery of her own. She becomes his front, the human face of their detective agency, while he pulls the strings from the shadows, using increasingly absurd and grotesque methods to extract confessions from suspects. What makes Neuro tick isn't justice or helping people. He's a selfish creature hunting for the next puzzle that will satisfy his supernatural hunger. Yako gets dragged into increasingly bizarre cases, from poisonings to blackmail schemes to crimes that defy logic entirely. The two bicker constantly, their dynamic fueled by Neuro's callous disregard for human suffering and Yako's attempts to maintain some moral high ground. This is mystery comedy where the supernatural detective is less hero and more chaotic force of nature.