When she was still young, Wilhelmina, a duke’s daughter, suddenly gained a younger stepbrother. Believing him to be her father’s illegitimate child, and seeing that he knew nothing about studies or etiquette, she treated him strictly while trying to teach him. Yet Nigel never once showed displeasure. On the contrary, he would follow her around every day, calling “Sister, Sister…” with deep affection—!? She thought he hated her… But he actually loves her? A slow-burning, overly affectionate love story between a quiet stepbrother who is far too obsessed with his sister and a strong-willed duke’s daughter.