My Stepsister Lets Me Put My Cock Inside Her, But Only the First 3cm - Akari Mitani (2020)

Mitani Akari’s younger brother had an incident and got injured. He cannot masturbate and the older Sister Akari pities him and decides to help him out. Naturally, things get out of hand, and when it all escalate to sex. But the sister imposes him a rule, he can only penetrate her 3cm deep……… Implying he had more than 3cm anyways.