Akuma-kun (ONA)
Japanese title: 悪魔くん
Type: ONA
Episodes: 12
Source: Manga
Genres: Horror, Supernatural, Suspense
Studios: Encourage Films
Producers: Toei Animation
Duration: 23 min per ep
Rating: R - 17+ (violence & profanity)

Millennium Research Institute, a counseling office where bizarre requests come in. The head of the research institute, Ichirou Umoregi, also known as "Akuma-kun," a genius boy who only appears once in 10,000 years. However, he doesn't know his real family. So Akuma-kun, along with his partner Mephisto III, pursue the mystery of his origin while challenging mysterious cases in this mysterious detective buddy story.

(Source: Fandom)