Pyra is a Blade, which are personifications of weapons used by Drivers. Blades are essentially immortal, only returning to their Core Crystals once their Driver dies. Pyra specifically is one of two legendary Blades known as the Aegis, a legendary Blade; Pyra has fire elemental abilities. Rex, the protagonist of Xenoblade Chronicles 2, becomes Pyra's Driver after she shares part of her life force with him to save his life after being mortally wounded. This link makes Pyra dependent on Rex's survival: if he were to die in combat, she would die with him. Rex vows to protect Pyra on their shared quest to find the paradise land of Elysium. Pyra differs quite drastically from Mythra. Pyra is very friendly, is an excellent cook, and fights more gracefully. In contrast, Mythra is more blunt, is a horrible chef, and fights heavy-handed.
In the aftermath of the Aegis War, Mythra was able to witness firsthand how much destruction her battles against Malos, the other Aegis, had caused. In anguish, she transformed into Pyra to cope with the consequences of her actions, splitting her personality. Addam, the prince of the Kingdom of Torna and her Driver at the time, traveled with Pyra to seal away Mythra's true sword that he was unable to control; then he put Pyra in stasis on the Ancient Ship and sank it under the Cloud Sea to prevent her from reawakening and losing control. 500 years later, Rex, a Leftherian salvager, was hired by the new terrorist organization known as Torna to bring up the Ancient Ship. Rex accidentally touches the core crystal of Aegis and is promptly killed by Jin, the antagonist of the game. Just before Rex died, he meets Pyra in a vision at Elysium. Pyra offers half of her life force to Rex to save his life if he helps her reach Elysium, to which Rex agrees. The two managed to escape Jin and go on an adventure to find Elysium. Along the way, they amass a party of other Blades and Drivers that have similar goals.
Early on in the adventure, Mythra leaves most of the fighting to Pyra, as she is afraid to use her power after the Aegis War. After Rex has a near death experience at the hands of Malos, Mythra is forced to reawaken and save Rex. After the battle, Pyra explains her past as an Aegis and her battles against Malos to Rex. After a while of reluctantly allowing herself to used in battles, Mythra becomes more open and willing to work with Rex, and the two eventually learn to swap between each other during a battle.
After many encounters with Torna, Jin eventually dispatches the party and attempts to kill Rex; Pyra ends up offering herself over instead to make sure Rex lives on. After Pyra is taken by Torna, Malos begins to siphon data from Pyra's Core Crystal to regain his lost powers, stealing much of Pyra's life force. Though faced with the setback, Rex and the group are informed of the third Aegis Sword that Addam and Pyra sealed away. At the end of the dungeon known as Spirit Crucible Elpys, they are able to find the sword, but it disintegrates in Rex's hand. Rex, now knowing what he must do, is unfazed and leads the party to where Pyra was taken. Malos reveals that with his powers now intact, Pyra has become a lifeless corpse. In the ensuing confrontation, Pyra and Mythra implore Rex to leave them behind; they reveal that, due to their guilt over the Aegis War, they wished to go to Elysium was to beg the Architect, the creator of Alrest, to let them die. Rex, however, assures them that they do have a place in this world and that he will continue to stand by them. In doing so, Rex summons the third sword and becomes the Aegis' true driver; Pyra then rises from the ground and takes on a new form known as Pneuma. With Pneuma and Rex's new powers, the group easily dispatches Jin and Malos.
After the battle, Rex, Pyra, and the others begin climbing the World Tree. They face multiple challenges on the journey up, including battles with Jin. With Pyra's newfound powers and Rex's ability as a true Aegis Driver, they are able to surpass these roadblocks and make it to Elysium. There they meet the Architect, a scientist named Klaus, whose experiments to create a new universe split the world into separate dimensions. Alrest's counterpart dimension is the world of the Bionis, where half of Klaus's consciousness resides as the evil god Zanza. Klaus reveals that Pneuma and Logos (Malos's original identity) were originally processor units on a device known as the Conduit. A third processor, Ontos, went missing in the accident that split the worlds (implying that Ontos is in fact Alvis, the personification of the Monado). After meeting the Architect, Rex, Pyra, and the others face one final battle with Malos, who seeks to destroy Alrest once and for all. Rex and Pneuma eventually deal a fatal blow to Malos, ending the conflict. However, the World Tree begins to collapse, and Pneuma offers to stay behind in order to destroy the World Tree before it crashes down and destroys Alrest, much to Rex's objection. She leaves Rex with her Core Crystal, thereby restoring his heart, and the party escapes as Pneuma self-destructs the World Tree. After the credits, Pneuma's Aegis Core Crystal begins to glow again, and Pyra and Mythra return, now in separate bodies although it is left ambiguous as to whether they remember Rex or have been reborn without memories as Blades usually are. The story ends with Pyra and Mythra rejoining the group as they travel towards a new land.
As a playable character
Main article: Pyra (SSBU)
During Ultimate's development, Masahiro Sakurai had considered adding characters from ARMS and Xenoblade Chronicles 2; however, as their games were announced after he completed the roster early in development in order to secure all returning fighters, he passed them over, choosing to have Pyra be a spirit instead. Years later, Pyra would be announced as the tenth DLC fighter alongside Mythra in the February 17, 2021 Nintendo Direct. A character showcase was streamed March 4, 2021 (March 5 in some time zones), with Pyra being released later that same day.
Names in other languages