Pikmin lost civilization
Years after Olimar last rescued Pikmin, the Pikmin race had been decimated by the planet's predators, such as Bulborbs and Dweevils. All the surviving Pikmin have been enslaved by the ultimate Dweevil, except for one clan of ten Pikmin. One day, a blue Pikmin was wandering around the current campsite and fell down a hole where he found strange symbols and a big empty space in the middle of the wall. When he went back up to the surface he asked the elder about the symbols.
The elder wanted to see the symbols, so he went with the blue Pikmin down the hole. The elder knew how to read the symbols. He said some words in a foreign language, and he wrote a symbol in the empty space. All of a sudden, the cave was filled with a bright light, which blinded the blue Pikmin and the elder. When they could see again the wall where the elder had written the symbol opened up, revealing an onion shaped like a bomb.
The onion sprouted one Pikmin. The blue Pikmin and the elder pulled the Pikmin. The Pikmin looked like a bomb. The bomb-shaped Pikmin told the visitors about a lost civilization where everyone was free.
And so, their adventure began to find the lost city.