The relationship between Yuta's mother, Tamaki, and his older sister, Yuuki, who he thought was a normal family, became strange because of something. Until just a little while ago, my mother, sister, and even my father took a bath together. However, one day my sister was played with by her friends, and the family relationship changed. A mother who can not help her sister who is played with and comforts Yuta who was depressed with huge breasts. After that, the mother, daughter, and four family members began to deepen their family ties by overlapping skin to skin.