Is Infinite Dendrogram 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
Action, Adventure, Fantasy, Video Game
In the year 2043, <Infinite Dendrogram>, the world's first successful full-dive VRMMO was released. In addition to its ability to perfectly simulate the five senses, along with its many other amazing features, the game promised to offer players a world full of infinite possibilities. Nearly two years later, soon-to-be college freshman, Reiji Mukudori, is finally able to buy a copy of the game and start playing. With some help from his experienced older brother, Shuu, and his partner Embryo, Reiji embarks on an adventure into the world of <Infinite Dendrogram>. Just what will he discover and encounter in this game world known for its incredible realism and infinite possibilities? (Source: J-Novel Club)
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