Is Accel World: Acchel World. hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

Special · 2012 · 8 episodes · PG-13 - Teens 13 or older
Comedy, Sci-Fi
Spin-off of Accel World included on the anime Blu-ray/DVDs.
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