MIDA-308 I accidentally witnessed my NEET shut-in sister masturbating and lost all reason. She came but didn't notice, wild piston under the moonlight.

"I saw it…." — My sister's room is messy and dirty. She has been wearing the same lame T-shirt since middle school. She reads erotic doujinshi and has bad eyesight. On top of that, she's a hikikomori and a NEET. A typical fujoshi... Of course, since we're siblings, I had no interest. ――Seeing my sister seriously masturbating! In that instant, my sense of morality, ethics, and reason collapsed with a sound. I turned into a lust monster for my sister! My sister's dry, mourning pussy also awakened! I kept repeating vaginal penetration and internal ejaculation…