Is Nijiiro Days: Houkago Special hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV Special · 2016 · 1 episodes · PG-13 - Teens 13 or older
Comedy, Romance, School, Shoujo
Recap of the first 12 episodes of Nijiiro Days.
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