Cheng had to be hospitalized because of a heart attack. There, he met the attending physician's daughter Yu, and became good friends ,Cocoon always visits him, and the two of them can always play together for a long time and spend a lot of happy time. At that time, Cheng didn't know how serious his illness was, so he always excitedly told Yu what to do together after he was discharged from the hospital, and Yu always agreed to him excitedly. Cocoon suddenly found out about his illness. One day, she went to her parents' room to get toys, and heard the adults discussing that Cheng was seriously ill and would die before he was twenty years old. Cocoon was very sad when she heard this, and decided to change such a sad thing, and she wanted to cure Cheng's illness. Cheng likes Cocoon very much. He always kisses her and always says that he wants to marry him. They will get married when they are twenty years old. During the summer vacation when he was twelve years old, Yu graduated from elementary school, Cheng went through the discharge procedures, and went on a graduation trip with Yu. During this trip, he knew his fate