Yuika Koga
On the outside, she is a cute and outgoing girl who is playful with her friends, especially Keiki. She can sometimes be childish and jealous when Keiki is around other girls, especially Sayuki. She does not get along with Sayuki and is always picking on her and the same goes both ways.
(Source: Kawaikereba Wiki)
However, on the inside, Yuika is actually a huge Sadist/Femdom. She wants to dominate Keiki and wishes for him to become her slave, the polar opposite of Sayuki.
