Is Garden of Remembrance hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

Movie · 2024 · 1 episodes · PG-13 - Teens 13 or older
An untidy room. Empty beer tins, empty wine bottles, a half-empty glass of whisky... A girl is getting up absent-mindedly and starts preparing herself. YOUR morning starts. Lazy and hard-to-wake-up YOU. The emoticon is ME watching over YOU. I play tricks on YOU, while YOU are playing the guitar and drinking. One day, in town, YOU walk past THE CHILDHOOD FRIEND who is buying an Anemone I liked, and remembering that I liked them, YOU rush out to buy them. THE CHILDHOOD FRIEND displays the Anemone with care. One day, years after I died, YOU hear noise from the closet. Opened, YOU see MY garden right in front of YOU. Overflowing emotions of ME and YOU. When exiting from the room with memories, a picture of the Anemone that YOU painted is displayed in YOUR new room. (Souce: Annecy Film Festival)
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