Is Gintama: Shinyaku Benizakura-hen hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

Special · 2010 · 1 episodes · PG-13 - Teens 13 or older
Action, Comedy, Historical, Parody, Samurai, Sci-Fi, Shounen
It's the running gag of Ben Johnson episode where animation staff reuse the New Years footage; Yorozuya would sit around the kotatsu eating a bowl of tangerines. They discuss elaborate subjects, Shinpachi complains about reusing animation footage, and then Gin-chan always ending the gag with a pointless announcement.
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