MIDA-308 I witnessed my withdrawn, virgin sister masturbating and lost my reason. I didn't notice my sister was cumming so I started pounding her like crazy.

"I saw it..." My sister's room is messy and she can't clean it up. She's been wearing the same ugly T-shirt since middle school. She reads erotic doujinshi and has poor eyesight. On top of that, she's a shut-in and a NEET. A typical "mourner girl"... Of course, since we're brother and sister, I wasn't interested. --But then I saw my sister masturbating in earnest! At that moment, my morals, ethics, and reason all collapsed. I became a sex monster, turned on by my sister! My sister's dried-fish, mourner pussy was awakened too! I ended up cumming inside her vagina over and over again...