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

TV · 2020 · 12 episodes · PG-13 - Teens 13 or older
Anthropomorphic, Comedy, Pets, Reincarnation, Seinen
In the "one-of-a-kind samurai-general-reincarnated-as-a-canine comedy," Nobunaga perishes at Honnouji as in history, and reincarnates in modern-day Japan as a dog named Shinamon. Other Warring States era warlords such as Takeda Shingen eventually join him, also as dogs. (Source: ANN)
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