Story: 

    Neuro is a Being from the underworld, who likes to eat "riddles" and "mysteries" and since he had heard that mysteries abound in the world above , he comes surface side in search of the ultimate riddle capable of satisfying his insatiable hunger
He arrives in front of Yako Katsuragi whose father has been murdered, and smells a tasty riddle ... and in turn helps her.
Neuro forces Yako to act as a detective and they together go in search of riddles to solve.