Despite having very different personalities, Zhengxin and Acheng are good friends. Nini is Acheng's beloved little sister, and Zhengxin loves and treats Nini as if she were his own sister too. However, their happy times together as two brothers and a sister soon end when Zhengxin suddenly leaves during high school and ceases to have contact with the siblings. It's not until 10 years later, when Nini goes to college, that she meets Zhengxin again as his neighbor. Nini soon realizes the always gentle and kind brother Zhengxin has a distressing secret, and Nini becomes determined to protect Zhengxin's wish...