The Nu Guardian is a Nu guarding Mount Emerald in the Lost Sanctum in prehistory. The party defeat him, but he swears to train and defeat the party the next time they meet. In the Middle Ages, the party hear that he's been waiting alone for a challenger for millions of years. They find and befriend him after a competitive battle.
Frog: Have you no companions? No people you wish to protect? Those are what drive a man to victory, not strength of arm.
Inspired by their words of friendship, the Nu helps one of the Reptites construct the Great Bridge, then returns to the sanctum to open up a shop selling high-quality items.