Iiyama Yumi

Masaki's older sister, a third-year student at the same academy. At the academy, she's the captain of the lacrosse club. Unlike her frail younger brother, she's athletically gifted and a dependable big sister type who's admired by her juniors.

However, she's incredibly lenient towards her brother Masaki, doting on him like a cat, to the point it's famous throughout the school. Those in the know say this spoiled Masaki's personality...

After hearing about her brother being horribly mistreated by a slut, she decides to take revenge on the two women and incites Masaki to join her.

She has no experience with men, but she has extensive lesbian experience with her club juniors. She harbors the desire to give her virginity to her brother, Masaki.