Twenty-two-year-old Su Wan suffers from dilated cardiomyopathy and severe depression, refusing treatment and seeking death. Lu Ye, a fellow patient in the same hospital suffering from terminal cancer, uses his gentleness and calmness to knock on her closed heart. The two watch the sunset on the rooftop and chat about trivial daily life late at night; romantic feelings quietly arise, yet love is hard to express when it reaches the lips. Lu Ye's condition takes a sharp turn for the worse. Before passing away, he signs an organ donation consent form without Su Wan's knowledge, leaving his heart to her. After surgery, Su Wan learns the truth, bearing immense guilt and longing, and strives to live on carrying Lu Ye's heart. However, the transplanted heart experiences rejection, and the heart muscle suffers irreversible necrosis. Her mother cannot empathize with her mental anguish, leaving her to endure the physical pain and indebtedness all alone.