Rika

From FairGame: A boy named Nishizawa Kazuya is in his second year of middle school. Unlike his younger sister, Rika, he is good at a lot of things and is the fastest runner in school. Parents and others think he is a responsible and hard working child. It seems that he is a perfect and good child but he has a secret that he can't tell anyone. Every day he enjoys taking a peek at his sister undressing herself.