Is Ninja Collection hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

TV · 2020 · 13 episodes · PG-13 - Teens 13 or older
Horror, Supernatural
Set in modern-day Tokyo where dreams and desires are afloat, a group of ninjas called "Toukeshuu" is set to stop the spread of "darkness" that prevails in the world using ancient techniques passed down through generations. (Source: MAL News)
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