Classmates Rion and Hiroaki are unusual for modern couples in that they have been in a pure relationship where they have only kissed so far. During summer vacation, Rion visits Hiroaki's relatives' house without her parents' knowledge. They have a lewd custom of 'tasting' the women who will become the lovers or wives of the men in the family. They set their sights on Rion's cuteness and beautiful breasts, and use various situations to seduce her. After having her small breasts thoroughly played with, she suddenly realizes that her masochistic nature has blossomed and she is beginning to desire sexual intercourse herself...