Is Imouto sae Ireba Ii. (ONA) hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

ONA · 2017 · 6 episodes · PG-13 - Teens 13 or older
Comedy
Original "chibi" styled animations of Imouto sae Ireba Ii. posted on the anime's official Twitter channel. Also included on the BD/DVD releases.
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