I went to Tokyo to take an exam and ended up staying at my brother's place for a while. One night, I accidentally saw my brother and his wife having sex. My sister-in-law was on all fours with her ass in the air, her face buried in my brother's crotch. I couldn't help but jerk off to the sight and finished. It seems like my sister-in-law found out... 'My younger brother-in-law is getting turned on by me...' Understanding it this way, my sister-in-law has been pouring all her lust onto me since the next day...
