Aion

Artifice Aion is the most powerful of the Artifices in Xenoblade Chronicles 2, capable of destroying Alrest, and the final boss of the game.

Story
Aion briefly stirs as Mythra uses a portion of Pneuma's power to battle Malos at Soaring Rostrum in the Kingdom of Torna.

Malos first learns of Aion's existence as he steals Pyra's memories to restore his Core Crystal at the Cliffs of Morytha. When Rex refuses to abandon Pyra and Mythra during their battle with Jin and Malos at Gotrock Oracle Ruins, their consciousness are transported to the Aion Hangar, with Pyra claiming Aion to be her true power. After their conversation, Pyra and Mythra fuse into their true selves, Pneuma.

Aion is later seen in a flashback in the year 20XX when the director of the First Low Orbit Station gives the order to activate Aion via the Conduit as a last resort to fight off the attacking Saviorite Rebels, only to be locked out by Klaus who plans to use the Conduit for his experiment.

As Malos is the first to reach Elysium, in preparation of piloting Aion to destroy Alrest, he sends down several and Sirens to attack Alrest. When the party confronts Malos at the Aion Hangar, they try to persuade him to stop, to no avail. Malos pilots Aion to battle the party. After a grueling battle, Rex, Pneuma, and Siren are able to defeat Aion, fatally wounding Malos in the process. As the party escapes the collapsing World Tree, Pneuma stays behind to use the last of Aion's power to destroy it and save Alrest.

As a boss

 * Artifice Aion (part 1)
 * Artifice Aion (part 2)