It tells the story of a pair of high school classmates who experienced a wonderful high school life together and fell in love in high school life. However, due to the willfulness of the male protagonist, they finally separated after the college entrance examination. After entering college, the male protagonist gradually grew into a real man in college life for four years. Finally one day, the girl came back to him, but as a friend. During this period, many touching things happened between the two of them. At this time, the male protagonist was no longer as naive as he was when he was young. Because he could not forget her, he still wanted to continue the relationship, but now he was at the bottom of society and was not worthy of saying "I love you" again, so he began to prepare to get a graduate degree and go to the city where the girl was. He came, but the heroine went abroad after graduation, so the hero was disheartened. After finishing school, he came to open a company with his friends. Just as his career was booming, he learned that the heroine had a very serious disease and could not find a suitable match. All the money in the family was spent, but the condition did not improve at all. In the end, the hero sold all his property and everything because of the illness of his beloved girl. He donated his bone marrow for her. When the heroine finally recovered from her illness, he only knew that he had a kind heart and donated money to her and found a bone marrow donor. The hero left the hospital before recovering. It was not until the heroine's wedding day that he attended her wedding and accidentally discovered that the groom was having an affair in the room. The hero beat him, and then he met the heroine. Only then did the heroine realize that he had never left her side.