The legendary treasure (or Great Treasure) refers to the large amount of treasure that Wario aims to steal from the Golden Pyramid in Wario Land 4. He first hears about the Treasure when he read a newspaper article, and he sets off towards the pyramid in his Wario Car in the middle of the night in the hope of having the treasure all to himself. When speeding through the city, he almost runs over a Black Cat. The newspaper article flies into her face, and she seems to read it with a curious interest. At the Pyramid, the Black Cat guides Wario to the main room. Here, there are five passages. The four main ones (Emerald Passage, Ruby Passage, Topaz Passage and Sapphire Passage) each have a Boss which guards a Great Treasure and three treasure chests. The boss Spoiled Rotten guards no Treasure. Cractus defends the Crown, Cuckoo Condor guards the Earrings, Aerodent wears the Necklace and Catbat protects the Bracelets. When each of these bosses are defeated, the treasure chests and the legendary treasure is collected and stored into the Golden Pyramid on the main map.
When all five bosses have been defeated, the Golden Pyramid will become accessible. This is the stronghold of the Golden Diva, the game's final boss and the evil ruler of the pyramid. The Golden Diva wears all of the ancient jewelry that was taken from the four bosses. There is also a wall with holds up to twelve treasure chests, three from each boss. If the Golden Diva is defeated, in a final wave of fury she will begin to destroy the internal structure of the pyramid, causing it to begin crumbling to the ground. Panicking, Wario gathers up the treasure and puts it into a sack, and makes an escape with the Black Cat leading the way out. When they reach a safe distance, they watch it crumble to the ground. The four Great Treasures that the Golden Diva was wearing fly out of the sack and return to the Black Cat who transforms into Princess Shokora, the true ruler of the pyramid. The Princess kisses Wario thank you and farewell. Four angels surround her, and they lift her into heaven. After sitting there for a short while trying to make sense of it all, Wario grabs what remains of the treasure, throws it into the back of his Wario Car and drives across the desert back home.
During the credits, various Gold Treasures fly out of the treasure sack and are shown to the player. For each treasure, Wario remembers a scene from his childhood.