Seventeen-year-old Eun-ha has battled a weak heart since birth but has managed to live a normal life following surgery. However, her world shatters when her doctor reveals that she has just one year left to live. On the very same day, Ha-yoon, her classmate, is admitted to the hospital due to a devastating car accident that claims the lives of his entire family. Overwhelmed by grief, Ha-yoon contemplates ending his own life, while Eun-ha is determined to embrace the remainder of her days for the sake of her loved ones. Although their circumstances differ greatly, Eun-ha senses a shared connection with Ha-yoon and tries her best to become his friend. With the clock ticking on their time together, are they doomed to say farewell forever?