Onion

The Onions are the nests of the Pikmin. Olimar named them so because of their resemblance to a vegetable native to his home planet. These bulbous plant-hives have brightly-colored bodies with a black-and-white band across the midsection. Three stilt-like legs suspend the Onions out of the reach of hungry predators, and provide access to the inside for Pikmin. In Pikmin 1, Olimar states that he inspected the Onion's legs, and saw they were covered with tiny little hairs. There are three known types of Onion, each with unique coloration corresponding to either Red, Yellow or Blue Pikmin, and only one of each has ever been seen. Subterranean Pikmin species such as Purple Pikmin, White Pikmin and Bulbmin do not have Onions, or at least none that have yet been discovered.

During the daytime, Pikmin hunt and bring food, such as pellets or slain beasts, to the Onion, which in turn produces new Pikmin seeds. If there are fewer than 100 Pikmin on the field, the seeds are ejected and take root in the ground, but if not, they are stored inside the Onion, along with any other Pikmin not on the field. When night falls and all the Pikmin have returned, the Onion folds its legs and lifts off from the ground, presumably using its flower petals like rotor blades to propel itself into the low atmosphere, where it hovers until daybreak. If an Onion loses all its Pikmin, it will produce a single seed the following day to prevent extinction.

When the Onions were first discovered in Pikmin 1, they were dormant. They had a dark grayish color, were flowerless, and their legs were buried in the ground until Olimar came upon them, at which point they sprang to life and spat out a single seed. It is not known exactly what triggers this hibernation, though it's possible that a loss of Pikmin, food shortage, or loss of captain may prompt the Onion to become dormant until conditions improve. In Pikmin 3 when multiple Onions are disscovered, the fuse into one Onion called the Master Onion.

Pikmin: Attack of the Breadbugs
Onions make an obvious reappearance in Pikmin: Attack of the Breadbugs. As before, Onions will follow the Captain's ship into the sky when nighttime occurs. Onions merge together as they do in Pikmin 3 when nighttime occurs and the ship flies off. However, Onions can only hold a million of each species. By farming one million of each type of Pikmin, it is possible to earn seven million Pikmin in total.

Pikmin Forever
Onions play a pivotal role in Pikmin Forever. A large cluster of Onions hangs over a specific location high above PNF-404, with which both the KHA Lander and Captain Olimar's rescue ship collide. Captain Olimar is saved by a Red Onion, which becomes the first Onion to join him in the game.

Onions have a similar appearance to their design in Pikmin 3, but the triangle pattern on their side is no longer present, and their legs are now roots that actually root into the ground. Onions can dematerialize into their roots and travel their essence through the ground; this allows Onions to re-materialize inside of caves alongside Olimar's ship. Onions retract their roots to fly up with Olimar's ship at night; Onions merge at this time with the same sort of dematerializing effect. There are five Onions in the game for the five major Pikmin types: Red, Yellow, Mushroom, Blue, and Lichen.