Maitreya Buddha enters Journey to the West through the crisis at Little Thunderclap Temple. The Yellowbrow Demon is actually a boy who served before him. While Maitreya was away, the boy stole the Golden Cymbals and the human-seed bag, descended to the mortal world, and posed as a Buddha in order to trap Tang Seng and challenge Sun Wukong.
The stolen treasures make Yellowbrow exceptionally difficult to defeat. The Golden Cymbals seal Wukong inside, while the bag swallows gods and fighters who come to help. After repeated failures, Wukong meets Maitreya, who explains the demon’s origin and devises a capture plan.
Maitreya disguises himself as a melon farmer and has Wukong hide inside a melon. When Yellowbrow eats it, Wukong torments him from within while Maitreya recovers the bag and subdues his runaway attendant. Maitreya’s personal intervention resolves a battle that celestial reinforcements could not win, and his relationship to both Yellowbrow and the two stolen treasures defines the entire episode.