Is Bio Hunter hentai?
No
Rated R+ (Mild Nudity) on MyAnimeList and not tagged as Hentai.

OVA · 1995 · 1 episodes · R+ - Mild Nudity
Action, Fantasy, Gore, Horror, Mythology, Seinen
In the molecular biology department of a major university, Komada and Koshigaya do more than just teach. They are also investigating demon viruses, which cause people to morph into grotesque creatures with a craving for human flesh. While conducting their research, the pair encounter Sayaka Murakami, the granddaughter of a famous fortune teller. Feeling compelled to help her find her missing grandfather, Komada and Koshigaya learn that a group of thugs is pursuing Sayaka. To make matters more sinister, these perpetrators seem to have a connection to the demon viruses. [Written by MAL Rewrite]
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