NFDM-532 Mizutani An: My Innocent Little Sister Forced into Golden Shower Slave Training

My innocent little sister suddenly started acting strangely after visiting our house. When I discovered her secretly having sex with my childhood friend, I got angry, but she burst into tears out of fear. After being punished by being locked underground, she claims she 'can't see anything wrong' and demands an escape. While being forced to watch videos of 'childhood friend sex,' she's violently abused until unconscious, then even made to hold in small urine. Eventually, she begins 'semen management' training, marking the start of their cohabitation life.