The main character of the series is Neuro Nougami, a demon who takes pleasure in consuming enigmas and riddles. He ventures into the human world to satisfy his hunger for the negative energy that emanates from premeditated crimes. Having to adhere to human customs requires him to maintain a low profile. To achieve this, he forms an unbreakable bond with Yako Katsuragi, who has her own mysteries to solve. Together, they team up to uncover secrets, crack cases, and feed Neuro's bottomless hunger.