Yellow Comet is one of the five major nations in the Wars World. They are antagonists in the first Advance Wars game, after which they ally with our heroes and join the Allied Nations.
Later, when Orange Star passes through their territory to get to Blue Moon, Yellow Comet's emperor, Kanbei, assumes a threat of invasion and declares war on Orange Star.
Later on though, Sonja, head of Yellow Comet's intelligence division, unearths the true mastermind behind the attacks on the three nations, Black Hole. Yellow Comet and the other four nations then team up to defeat Black Hole.
Advance Wars: Days of Ruin