KIMI TO HANABI TO YAKUSOKU TO

The story centers on two Tokyo high schoolers who connect over a painting of fireworks. They trace the painting to the Nagaoka Fireworks Festival in Niigata, one of Japan's three major fireworks festivals, and to a mysterious promise that connects the two to the past. (Source: Crunchyroll News, edited) — Description from AniList community (anilist.co).