Kanpeki Ojousama no Watakushi Episode 4

Student council presidents are often respected or even feared by the students at their school. Combine these traits with an astonishingly beautiful appearance and you get Irina Shirogane—a seemingly perfect student who everyone looks up to. However, looks can be deceiving, as president Shirogane bears a carnal secret: she is an extreme masochist with an insatiable lust. One day, Sado Yuuji walks in on Shirogane as she pleasures herself in a classroom. As a result, each time Sado crosses her at school, he sports her a look of disapproval. Turned on by the prospect of being looked down upon, Shirogane decides to confront him, only for her masochist impulses to lead the two into a sexual encounter. Thereafter, she decides to make Sado her master—and thus begins a rather unconventional relationship. [Written by MAL Rewrite]