The narrative builds on a foundation of dual secrecy. While Seo-yoon’s secret is her daily anterograde amnesia, Jae-won hides a far more fatal truth: he suffers from a congenital heart defect inherited from his late mother.
As their relationship deepens, Jae-won’s physical health deteriorates. Realizing his life is short, he makes a heartbreaking request to Seo-yoon’s best friend, Ji-min: if he dies, Ji-min must remove every photograph, diary entry, and drawing of him from Seo-yoon's room. Jae-won knows that if Seo-yoon wakes up every morning with amnesia only to read in her diary that the love of her life died, she will experience fresh, devastating heartbreak every single day.
Midway through their high school year, Jae-won suffers a sudden cardiac arrest and passes away. True to her promise, Ji-min erases all physical records of Jae-won from Seo-yoon's journals. The next morning, Seo-yoon wakes up with no conscious awareness that Jae-won ever existed.
However, her subconscious mind resists the erasure. Seo-yoon finds herself constantly sketching the face of an unfamiliar boy in her sketchbook. Driven by emotional distress and realizing that Seo-yoon is grieving an unknown ghost, Ji-min breaks her promise. She hands back Jae-won’s hidden drawings, photos, and his original notebook to Seo-yoon.
Seo-yoon reads Jae-won's words and visits his father and their favorite coastal spots. Standing by the ocean where they once laughed together, tears stream down her face. Even though her brain cannot retrieve the daily memories, her heart and senses fully recognize him. The film ends on a poignant note as she chooses to love and carry Jae-won in her heart every day moving forward.