During a three-day stay at his best friend's home, the friend's unusually touchy older sister Unpai teases him until he unexpectedly ejaculates. When she realizes he cums quickly but stays hard, she turns him into her personal cum toy, stroking and licking his cock whenever she gets the chance. They have sex beside his sleeping friend and in the bathroom, while she catches him for handjobs and blowjobs in the hallway and secretly sucks him during breakfast. After 30 ejaculations, he begs that he has nothing left.