Witnessing my NEET sister masturbating caused my rationality to collapse. Ignoring her already climaxed and wildly thrusting, I... (Moon Cloud Night MIDA-308)

"I saw it..." My sister's room was a mess. She'd worn the same ugly t-shirt since middle school. She liked reading erotic fanfiction and had terrible eyesight. Worse still, she was a shut-in and a NEET. A typical "loser girl"... Of course, since we're siblings, I wasn't interested. —Then I saw my sister seriously masturbating! At that moment, my morality, ethics, and reason collapsed. I became a sex monster seduced by my sister! Then, my sister's dry, useless little hole was awakened! I ejaculated inside her again and again...