整部动漫讲述的是以“谜”作为食物的魔界变种生物食脑奈罗，在将魔界所有“谜”都吃完后转而前往人间，去找寻更加极致的“谜”而发生的一系列故事，所谓的“谜”，其实就是一个个充满恶意的谜团在被破解之后会产生大量的能量，这些能量就是食脑奈罗的粮食，而“充满恶意的谜团”指的就是小到恶作剧，大到杀人行凶等充满恨意的事件，奈罗初次来到人间就遇到了父亲被杀害的高中女生桂木弥子，于是露出真实面目让弥子强行成为其在人间的代理，之后弥子不仅成功破解了父亲被害的真相，还同奈罗开了一家侦探事务所，在这过程中弥子也从被迫听从奈罗指示行动，到开始对“谜”产生兴趣，主动去采取行动，而奈罗也开始认可了她的能力，但是依旧每次破解谜团还是将弥子整的半死

The whole anime tells about the brain-eating brain-eating creature Nairo, a mutant creature in the Demon Realm who uses "mysteries" as food, and eats up all the "mysteries" in the Demon Realm. Afterwards, he turned to the world to find a series of stories about more extreme "mysteries". The so-called "mysteries" are actually malicious mysteries that will generate a lot of energy after being solved. Nairo's food, and "malicious mysteries" refer to incidents full of hatred ranging from small pranks to murders. When Nairo came to the world for the first time, he met Katsuragi Yako, a high school girl whose father was killed. The true face forced Yako to become his agent in the world. After that, Yako not only successfully cracked the truth about his father's murder, but also opened a detective agency with Nairo. Began to become interested in the "mystery" and took the initiative to take action, and Nairo also began to recognize her ability, but every time she solved the mystery, she still killed Miko