By chance, I noticed my younger sister, Kana's, laptop was left open. I casually glanced at the screen to close it. What was displayed was an erotic novel. Furthermore, the theme was 'Brother and Sister'. While feeling bewildered, I scrolled through the text...and noticed something odd. She wasn't reading it; Kana was writing it. Having learned my sister's secret, I tried to apologize to Kana, but──