Kodomo Atsukai Shinaide Kudasai! – Youjoka Shichatta Kanpeki Shukujo wa, Kishi Danchou ni Amayakasareru

Lady Rose, known as the "Perfect Lady," is constantly stressed by her troublesome older sister, childhood friend, and fiancé. When her frustration peaks, she mysteriously transforms into a child. The only time she finds peace is with Yuen, the knight commander called the "Smiling Prince." In her child form, she confides in him—but he seems strangely interested in the adult Rose.