Grimm Douwa: Kin no Tori

A golden apple is taken from the King's garden, prompting him to assign his three sons to protect the apples and identify the thief. The youngest son, Hansu, finds a feather from a golden bird that stole the apple, and as a result, the King sends his sons to capture the bird, beginning Hansu's journey. The film was completed in 1984 but remained unreleased for three years before its theatrical debut.