Rion and Hiroaki, classmates, were rare among modern couples, having only kissed and maintained a pure relationship. During summer vacation, Rion secretly visited Hiroaki's relatives' house without her parents' knowledge, but they had a depraved custom of 'tasting' all the women who would become lovers or wives of the men within the clan. They targeted Rion's cuteness and beautiful breasts, trying to lure her into various situations. After being thoroughly teased for her small breasts, she unwittingly developed a masochistic nature and began to desire lewd intercourse herself...
