Hazuki (27), the older sister, and her younger brother Shogo (25), decide to try a close-contact oil massage together as a fun sibling activity. Hazuki's glossy, oil-slicked body and soft skin prove irresistible, and Shogo, who happens to still be a virgin, quickly develops an iron-hard erection. Seeing him so aroused unexpectedly excites Hazuki as well. Caught in a strange mutual arousal, they end up having bareback sex, with Shogo sliding smoothly inside her. In a secret place they can never tell their parents about, they engage in creampie sex. The thrill of taboo draws them even closer, pushing both to multiple intense orgasms, until the session ends with the oil dripping and squelching noisily all around them.