Is Kaitou Tenshi Twin Angel hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

OVA · 2008 · 2 episodes · PG-13 - Teens 13 or older
Mahou Shoujo
Haruka Minazuki and Aoi Kannazuki are freshman high school students and best friends. During the day they help with school activities but at night they thwart enemies like Black Auction and other villains as Red Angel and Blue Angel, the Twin Angel team.
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