Big Fish & Begonia is a visually stunning animated film that tells the story of Chun, a young girl who transforms into a dolphin to explore a mystical realm. Along the way, she discovers the power of friendship, self-sacrifice, and the importance of preserving the natural world. Set in China, the film combines elements of fantasy, romance, and coming-of-age themes.

The story follows Qiu, who is resurrected by a spiritual woman to become the new Beidou Rushenglou. As he carries out his duties, he encounters a young man, and together they face a disaster that intricately links their fates to the world.

The young man becomes the new Nan Dou of the underwater world, but is unexpectedly involved in the Ru Sheng Lou mystery. The mysterious power leads the young man on a fateful journey, and he gradually uncovers the mystery, opening a new chapter in the underwater world.