Seeing his sister in a state of conflict and confusion, his older brother Joon-hee remembers that when he went to the nursery with his mom and dad, he mischievously dropped the sign with the newborn's name on it, and was particularly distressed by this. In the end, for the sake of the future, the two children go back to their real home and live a completely different life than before. Later, Prof. Yoon's family left for the US and Eun-hee began her difficult life.
Time passes and Eun-hee works as a telephone operator in a hotel. She meets Tae-suk, the youngest son of the hotel manager, by chance. Tae-suk develops a crush on Eun-hee and makes a serious advances, when Joon-hee returns from the United States. Tae-suk, Joon-hee, and Joon-hee's fiancée, Yumi, used to be close friends in the United States, where they studied together. After a few misunderstandings, Eun-hee and Joon-hee started to see each other frequently, and Joon-hee's feelings for Eun-hee changed from his original attachment to his sister to a strong love, but the thought of his fiancée, Yo-mei, caused him great pain.
When his parents found out about this, they expressed their strong disapproval, so the two went to the ranch, because of which Yumi attempted to commit suicide, and Tae-suk came to the ranch to look for them, so they had to come back with Tae-suk. Both of them are in a lot of pain, but they are still struggling hard to get back to their old state. Eun-hee discovers by chance that she has leukemia, and even Tae-seok starts to be intentionally distant. After learning about Eun-hee's condition, Tae-suk decides to be responsible for Eun-hee and vows to cure her, showing his selfless love for Eun-hee without any conditions. On the other hand, Joon Hee doesn't know about Eun Hee's condition and although he is with Yumi, he is only thinking about Eun Hee and he tells Yumi: don't go to the US and stay with him for six months, that's all he can do now. Joon-hee especially regrets losing Eun-hee, he drinks and tortures himself again and again. Back at home, Eun-hee is admitted to the hospital for fainting, and is well taken care of by Tae-seok, who agrees to his proposal for specialized treatment. She told her family that she had found a job at a Seoul hotel and left home.
Eun-hee went to see Joon-hee for the last time, but she hid the truth, saying that she wanted to go to a new place with Tae-seok to start a new life, and that she would live a good life, so that Joon-hee would not worry. Joon-hee says that she regrets breaking up with her so much. Eun Hee was admitted to the hospital and underwent a specialized bone marrow test. After Eun-hee left, Jun-hee waited for Eun-hee to contact him. Later, he learned from the phone recording that Yumi's hand injury had healed, and Yumi confessed to him: she was afraid that he would leave after her hand injury healed, so she kept it from him. Joon-hee needs some time to sort out his feelings before he goes to the US and he goes back to the ranch. When Tae Suk hears that a bone marrow transplant can cure the disease, he confesses everything to his family and asks them to never keep it a secret from Joong Hee since it's Eun Hee's intention. Eun-hee, who is in pain, also comes to the ranch and meets Joon-hee, who came first. She says she wants to spend the day with him while he says he wants to spend forever with her. Eun-hee hid her condition until the end, and she whispered in her heart, I'll always love you, and said her final goodbye to Joon-hee.
Back at the hospital, Eun-hee's condition continues to deteriorate and she falls into a coma. After a few hesitations, Yumi still tells the truth to Joon-hee. Jun-hee, who rushed to the hospital, cries and says that he still has words he hasn't said, which is: I love you, Eun-hee. Joon Hee painfully remembers all the images of his time with Eun Hee. He says to Yumi: Let's go back to the US together, even if Yumi doesn't go back, he'll go back himself. Yumi doesn't think that's what Joon-hee really thinks and thinks it's all her fault. The doctor says tonight is critical and tells everyone to stabilize their emotions. The family is feeling despondent, and Yeon-Ae thinks it's because she swapped fates with Eun-hee that this happened, and that Eun-hee got sick instead of herself herself, and for that she blames herself. Tae-suk suggests that Joon-hee go to the hospital with him, and Joon-hee cries that if Eun-hee sees herself, she might feel relieved and maybe just walk away, so she can't go.
But it turned out he went anyway. Eun-hee surprisingly awakens in front of Joon-hee, and the two decide to revisit the beach where they used to play together in their childhood in order to make some last memories in order to spend their last hours together***. In the end, Yumi decides to study abroad alone, and Eun-hee often holds back her injuries in order to spend her few remaining moments happily with Joon-hee, a look that saddens Joon-hee even more. Eun-hee starts to vomit blood and her condition worsens day by day. Once by chance, she finds a medicine bottle in Joon-hee's room, which turns out to be the medicine Joon-hee quietly prepared for himself as he feels he can't live without Eun-hee. Eun-hee told a tearful Joon-hee, Please don't ever die for me like a fool.
In the end, the two went back to the beach where they used to play as children, and Eun-hee went quietly on Joon-hee's back. Joon-hee couldn't withstand the heavy blow, and fell into a very disillusioned state, and finally perished under the loading truck.