Is Gundam vs Hello Kitty hentai?
No
Rated G (All Ages) on MyAnimeList and not tagged as Hentai.

ONA · 2019 · 3 episodes · G - All Ages
Comedy, Fantasy, Kids, Mecha, Sci-Fi, Space
While preparing for a tea party, Hello Kitty receives a distress signal from Haro. She travels to the Universal Century timeline to help Amuro Ray and the Gundam end the One Year War. Cross-promotion to commemorate the 40th anniversary of Gundam and the 45th anniversary of Hello Kitty. (Source: ANN)
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