MIAA-057 While masturbating, she was discovered by her sister-in-law and it ended

My younger brother (me) is beautiful but gets aroused all the time despite being bullied by his stubborn older sister. It seems like she's getting married soon, but I know that my sister was once a yankee bitch and pervert in the past. I will use this as a joke to force my sister to do it! Until now, I've been spying on sex with men, and it's time to give the results of my research on how to make my sister feel and cum.