APAK-100 JK's younger sister brought a middle-aged man to her room and peeked at her having muddy perverted sex... Akane Kuramochi

Unbeknownst to her brother, her younger sister, Akane, has grown into an adult, learned nasty things, and brought a middle-aged man older than her brother home. I think that my brother is absent and I work hard with a middle-aged man in my room. My brother pretending to be absent looks into my sister's room and erects after seeing sexual intercourse with a middle-aged man. What is the action taken by my sister, Akane, on the condition that her brother, who was peeking, shut her mouth?