Is Ame to Shoujo to Watashi no Tegami hentai?
No
Rated G (All Ages) on MyAnimeList and not tagged as Hentai.

ONA · 2005 · 1 episodes · G - All Ages
Romance
Katari, a young girl who dreams of becoming a novelist, writes a love letter to a boy at her school. Unwittingly, she is creating a "short story" that will move a little girl's heart.
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