Is Ai Yori Aoshi: Enishi - Miyuki hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

Special · 2003 · 1 episodes · PG-13 - Teens 13 or older
Comedy, Drama, Ecchi, Romance, Seinen
Ai yori Aoshi: Enishi - Miyuki is a 16 minute Christmas special set before the beginning of the first season. Based on manga chapters 43-44 and would also fit as episode 21.5 of the first season.
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