Is One Piece: Episode of Alabasta - Prologue hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV Special · 2011 · 1 episodes · PG-13 - Teens 13 or older
Action, Adventure, Fantasy, Shounen
An adaptation of the Whiskey Peak arc exclusive to some TV airings of One Piece: Episode of Alabasta.
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