Is Gintama x Mameshiba hentai?
No
Rated G (All Ages) on MyAnimeList and not tagged as Hentai.

CM · 2013 · 6 episodes · G - All Ages
Comedy, Parody, Shounen
Gintama x Mameshiba aired as a commercial to promote the Gintama: Kanketsu-hen - Yorozuya yo Eien Nare movie. Gintoki, Kagura, and Shipachi have turned into "weird living creatures," parodying the short kids' anime Mameshiba that features sword bean-dog hybrid creatures.
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