A first-year junior high school student named Makoto Natsume living in Chōfu, Tokyo, is caught completely off guard when a fellow freshman, Aki Hayama, suddenly confesses to him. The confession is puzzling not because of any lack of feeling on Makoto's part, but because Aki explains that her grandmother once told her she would meet a boy named Makoto Natsume in the future. Makoto is certain Aki has mistaken him for someone else, as they have never met before. Their unexpected connection deepens when Aki shows him a mysterious painting of a fireworks display. Intrigued by this clue, Makoto agrees to help her find the unknown Makoto Natsume she is searching for. Their investigation leads them to suspect the painting is linked to the famed Nagaoka Festival Grand Fireworks Show in Niigata Prefecture, one of the largest fireworks displays in Japan. The following year, the two travel to Nagaoka together, hoping to uncover the secret behind the artwork. What they find there is a mystery that connects them to a past promise that transcends 81 years, a promise tied to the city's history and the fireworks festival that commemorates it. As they delve deeper into the painting's origins and the reason Aki was told to find Makoto, the two young students are drawn closer together by fate. The story is a coming-of-age romance set against the backdrop of the Nagaoka fireworks, a festival that carries the weight of World War II remembrance. The central characters are Makoto, a boy described as lacking social skills and self-confidence, and Aki, a popular and talented girl who serves as her class's president. Together, they follow the mystery of the fireworks painting and must make a choice that will determine their future as the festival approaches.