先っぽ3cmまでは挿入させてくれる姉とのギリギリ相姦未満生活 美谷朱里 (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.