Is Minami-ke Natsuyasumi hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

OVA · 2013 · 1 episodes · PG-13 - Teens 13 or older
CGDCT, Comedy, Seinen
Second Minami-ke OVA bundled with the 11th volume of the manga. Chiaki, Kana, and Haruka decide how to spend their last few days of summer together. Kana struggles to finish her homework.
View on MyAnimeListShare
Check another title