Majin Tantei Nougami Neuro [Manga]

Nougami Neuro is a mystery eating demon from hell, dissatisfied with hell’s mysteries, Neuro heads to our world to try and find “The Ultimate Riddle.” To avoid publicity, he forces Katsuragi Yako, a japanese high school girl, to play the role of a detective, while Neuro masks himself as her assistant. Along the way, the two encounter many murders and odd characters.