For those who have not completed games in the Xenoblade Chronicles series, this page contains spoilers regarding the plot. Discretion is advised.
The Machina are humanoid beings with a machine-like appearance. Much like the Homs that are born of Bionis, these creatures are born of Mechonis. They can live for thousands of years (many of them watched the battle between Bionis and Mechonis). They do not need to feed on other life-forms to survive; they only require "a little water and some Ether every now and then."
Oddly, they also mention that water makes them weak, though it can be assumed that they are simply saying that they cannot be submerged in water or swim well, likely due to their mechanical parts and their weight.
There are events that show that Machina can attach certain equipment to augment their bodies.
War of the Titans
The Machina developed a religion based on their creator, Meyneth, who they worship throughout the game. They created a highly advanced civilization, and made friendly approaches with the people of Bionis. They maintained a peaceful age until Zanza took over the giant Arglas and attacked Mechonis and the Machina's capital, Agniratha, using Bionis and Telethia. Almost all of the Machina were wiped out until the titans grew weak and the attack ended. Exhausted from the battle, Meyneth went into a deep sleep to regain power, not before warning the surviving Machina that Bionis was not dead, and some day it would awaken once more.
One of the Machina, a young man named Egil, swore vengeance on Bionis and Zanza for the death of his companions and the possession of his friend, Arglas. To this end, he used the Mechon to attack the people of Bionis, which alienated him from his fellow Machina. After being displaced from their capital, they took residence on the Fallen Arm, where they tried to stop Egil. Unfortunately, Egil won the battle and the Machina were forced to hide their existence.
The party discover the Machina by chance whilst they are attempting to regroup after falling off of Sword Valley. They are taken into the Hidden Machina Village, where Fiora is treated to maintain her life with her new body. Shulk is then approached by the leader of the Machina, Miqol; Egil's father. He asks the party to kill Egil to stop the bloodshed, requesting that they first find Egil's sister, Vanea.
The party meets Vanea in Mechonis Field, after they are almost killed by Jade Face, and she guides them through Mechonis up to Agniratha. Egil is met for the first time in person at the Meyneth Shrine, and the party fight him and lose - they then must travel to the Mechonis Core, where he is fought again.
The destruction of Mechonis does not affect the Fallen Arm, so the Machina are largely unscathed from the events in Mechonis Core. Miqol continues to assist the party, taking care of Shulk and making him the Replica Monado to replace his missing sword. He offers to take the party to Bionis' Interior after the events of Colony 6.
It is noteworthy to say that Colony 6 will grow to have Machina immigrants. So far, there are no problems between the Machina and the races of Bionis, even though this is the first time as a fully integrated town with mixed races.
Although the Fallen Arm still exists in the new world, it is unknown if the Hidden Village stills exists or if the Machina will relocate again.
- According to a Colony 6 resident after a quest with Neonik, Machina are more vulnerable than Homs and get sick more easily.