The story centers on Kaito Hayashi, a calm, cool, and athletic boy who carries the weight of a tragic promise. On his birthday during his first year of middle school, he lost both of his parents in a devastating accident. At the hospital, with his mother's final breath, she asked him for a promise-one that would define the rest of his life. Ever since that day, Kaito's personality changed, closing himself off from the world around him. Now in high school, Kaito is determined to fulfill the vow he made to his mother. But as he navigates the challenges of adolescence, friendship, and love, he finds himself drawn to Hikari Sakuragi, a once vibrant girl who has retreated into her own darkness. Together, they may discover that keeping promises-and healing-means letting others in.