A 72-hour record of having sex with his girlfriend's H-cup sister from morning till night during a family trip that lasted less than 3 days. (SSIS-309)

Before my girlfriend went on a trip, her older sister came to visit, and the three of them chatted about the past until late at night. The next day, after my girlfriend left, only her sister and I were at home, and she suddenly confessed her feelings to me...