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

TV · 2023 · 3 episodes · PG-13 - Teens 13 or older
Avant Garde, Comedy, Mecha, Parody, Sci-Fi
While the adults have no hope for tomorrow, the youth accept the decline and poverty of the city as an ordinary part of their reality until Haruko throws the city into chaos. (Source: Anime News Network)
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