HBAD-262 My little sister has been acting strange lately… My sister being trained by her new big brother Satou Airi

Mother remarried. She never liked her new father and brother. The older sisters look at her brother with curiosity, and her mother is always flirting with her father. One day when I came home from school, my sisters were having sex with my brother. My older brother found me, who unintentionally stared at me, and forced me to do it. Then the training involving the family by my brother began.