This summer, my father remarried. After divorcing many years ago, he had raised me alone, and now he was starting a new chapter in his life. I was genuinely happy for him. His new wife had a daughter named Aoi, and at first, I felt awkward suddenly having a younger sister close to my age. But Aoi was cheerful and lively, and I quickly grew close to her, becoming like real siblings. Our once lonely household became warm and bright. My father and I were enjoying our happy days—until the day I accidentally peeked into my father and stepmother's room. That moment changed everything.