Shirakawa Sayuki

A classmate of Rikka's. Serving as class representative, she lives with her grandfather, who is apparently descended from samurai who once defended a castle.

Her name combined with her noble lineage has earned her the nickname "Snow White" (白雪姫).

Additionally, being both beautiful and brilliant, a scholar and an athlete, she’s been touted by many as the second coming of "The Perfect Lady".

In no time at all after her enrollment, these abilities result in her being entrusted with the role of Chairman of the Environmental Improvement Committee, which is essentially the academy's student council.

[Translated from post with info from Dengeki Hime]