MIAA-506 I'm losing my sense of rationality when my smug sister's underpants go bare.

My parents remarried and had a sister who was cute, serious and good... wearing t-shirts, and her conscious naked underwear lured me to go crazy, M-legged, tight-assed, tight-assed ass like this, and couldn't stand it, and from that day on, my sister would show me and laugh at it and get excited... and walk out of her pants to the bottom of her feet, the transparent underpants to the t-shirts to the t-shirts to the t-shirts to the t-shirts, the little demon to the t-shirts to the point of sexual intercourse.