Is It's a Rumic World: 50th Anniversary Weekly★Shonen Sunday hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

Special · 2008 · 1 episodes · PG-13 - Teens 13 or older
Comedy, Sci-Fi, Shounen
The characters from Ranma 1/2, Urusei Yatsura, and Inuyasha all gather together in a short crossover to introduce the 50th Anniversary Weekly Shonen Sunday "Rumic World" Museum opening, celebrating Rumiko Takahashi's manga work.
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