MIDA-308 I witnessed my older sister, a reclusive virgin, masturbating, and I instantly lost my mind. I didn't notice she had already orgasmed, so I started fucking her wildly. - Tsukigumo Yoru

"I saw it..." My sister's room was a mess. She'd been wearing that ugly T-shirt since middle school. She liked reading doujinshi, and her eyesight was terrible. Worse still, she was a total otaku and a NEET. A typical "mourning girl"... Of course, since we're siblings, I wasn't interested. Then, I saw my sister seriously masturbating! At that moment, my morals, ethics, and reason all collapsed...