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

ONA · 2018 · 10 episodes · PG-13 - Teens 13 or older
Boys Love, Drama, Sci-Fi
Gazing at the scenic view of the sky, a man is joined by a stranger who informs him that he is in a dream. Unable to recall the memories of his life, he relies on the visitor to take him on a journey of discovery. Revealing everything—from their seven-year relationship to the emotional hardships they faced together—the two rekindle their bond severed by time. Behind this beautiful love story, however, lies a much darker truth. [Written by MAL Rewrite]
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