Yuuta Yamauchi is a median excessive college scholar making ready for assessments via his summer time season vacation. His older cousin Kei Higashide, who takes pity on him as her "little brother," devotes her time and staying power to instruct this relative in need. One day, Yuuta manages to take a picturegraph of his classmate and crush, Youko Kaji, as a gust of wind lifts her skirt. When Kei reveals out approximately it, she laughs at Yuuta`s juvenile infatuation and begins offevolved teasing him approximately his sexual preferences. From phrases to deeds, she gives him her very own grown-up body—and Yuuta quick takes gain of the opportunity. As summer time season passes on and the family begin playing greater time together, their to begin with bland tutoring periods quickly change into a passionate and fiery relationship.