Seiyuu: Takeito Koyasu

The title character of the series, Neuro is literally a detective from Hell (Makai). He looks for mysteries and the labyrinthine mind for sustenance. As he explains it, when he dismantles the mystery and strips the culprit of all of their defenses, that releases the negative energies that caused the culprit to commit the crime, which he then consumes. He came to the human world in search of the Ultimate Mystery, as all of the mysteries in Makai were bland and repetitive. Once in the human world, he adopted Yako as his assistant, and began to solve mysteries. He does this because there's a rule in Makai that when the Makai inhabitants go to the human world, they must keep a low profile. In public Neuro makes Yako act as the detective, while he acts as her assistant, even though Neuro is actually doing all the detective work (though Yako occasionally figures things out herself as well). In the human world Neuro needs to sleep for three hours a day, which he spends on the ceiling. According to Neuro "Shouki is like Oxygen to a demon" and hot springs are formed when excess Shouki comes to the surface, so the best place for him to sleep is a hot spring. As Yako points out, he comes to the human world because eating is more important to him than oxygen.