Prison School Vol. 20

Hachimitsu Academy is a prestigious and strict private all-girls school on the outskirts of Tokyo that for the first time is admitting male students for the new academic year. However, only five boys are admitted: Kiyoshi Fujino, Takehito “Gakuto” Morokuzu, Shingo Wakamoto, Jouji "Joe" Nezu, and Reiji "Andre" Ando, meaning that the girls outnumber them 200:1. Though they at first think that their adolescent dreams have come true, they quickly learn that the school is ruled by the Underground Student Council and their harsh draconian laws. After being caught trying to sneak a peek into the girls’ bathing area, the boys are sentenced to imprisonment in the school’s Prison Block run by a sadistic warden who also happens to be the vice president of the USC. Now the boys must spend a whole month in the Prison Block or face expulsion.
In Vol. 20, the sports festival is in full swing and Hana sets her sights on beating Lisa at the obstacle course, but when her underwear prevents her from performing up to par, she has no other option than to change underwear with Kiyoshi in the middle of the crowded field!
Notice: This manga is written in Japanese.