Is Tantei Opera Milky Holmes: Alternative hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV Special · 2012 · 2 episodes · PG-13 - Teens 13 or older
Comedy, Detective, Mystery, Parody, Super Power
Milky Holmes is a detective team composed of four girls who descended from famous detectives and possess supernatural powers known as "Toys". In this alternative world, instead of losing their Toys and becoming worthless students, they are on the path to becoming successful detectives. Under the guidance of Kobayashi Opera, they work to solve mysteries. (Source: AniDB)
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