[Chinese]FNS-176 Her giant tits zombie NEET sister became my jerk-off material me

My girlfriend's older sister is a shut-in. Even when I occasionally see her at her house, we only exchange greetings, but she always looks at me with a cold stare like the representative of gloomy characters. One day, I accidentally caught her masturbating… Her usually plain-looking sister has an erotic body with huge tits, hourglass figure, and big ass! From that day on, we became mutual masturbation partners in secret!