At home with my beautiful girlfriend's sister

A guy went to his girlfriend's house to celebrate her birthday the night before, but the next morning his girlfriend went camping with her class. He lives far away so he asked to temporarily stay at the Tsumugi sisters' house for a few days, so right now it's just him and this girlfriend's older sister. Ever since his girlfriend was away, he had been plotting to have sex with this beautiful sister Tsumugi. He peeped at her bathing, smelled her underwear, and when Tsumugi came home from the market and discovered something unusual, this guy hugged her, kissed her, and raped her. During these few days, Tsumugi became a sex-crazed whore after he hit her sexual nerve, she was so lustful.