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

My girlfriend’s older sister is a recluse.When I meet her at her house once in a while, I only say hello, but she looks at me with stern eyes and is like the representative of a negative person.One day, I witnessed my older sister masturbating… She usually wears plain clothes, but I got a full erection on her erotic body with huge breasts, curvy neck, and big butt!From that day on, we started masturbating with each other without telling her!