Sugi and Anne, a father and daughter pair, shared a close life together. Sugi, once a sculptor, gradually lost his memories after being diagnosed with Alzheimer's. At his funeral, Anne imagines him crossing the mythical River Lethe, where souls forget their past lives. Through a symbolic journey via sculptures and fading memories, Lethe becomes a poetic visualization of remembrance, loss, and farewell—offering comfort to the filmmaker’s own familial grief. Inspired by Rodin's Gate of Life and Memories and TJ Dema’s poem Lethe, the film explores the emotional textures of memory and forgetting in a stylistically rich animated world.