Top 9 in Top 10 best 18+ anime for hot summer.
Prison School Trailer
Prison school is an 18+ anime based on the "Kangoku Gakuen" series, about a male high school student who enters an all-girls school. Originally, this school was for elite girls outside Tokyo.
All the trouble happens when the school allows boys to attend, but ironically a giant school has only five boys and a whole year has never heard of the weird rules, until they were locked up in "School Hell" while peeping at schoolgirls bathing and were caught by the sorority leader. In order to escape from this place, the five boys must overcome many difficulties and challenges.