Before Kingdom Hearts χ
Luxu is given a Keyblade forged from his own heart by the Master of Masters, who takes him, Ava, Aced, Gula, Invi, and Ira as his apprentices. Luxu eventually achieves the rank of Keyblade Master alongside his fellow apprentices.
Luxu frequently meets with the Master in the Control Room, where the latter recounts an ongoing Keyblade War that began in his youth and is about to end, in which the world would be destroyed and then rebuilt. Luxu is shocked that the Master was leaving the fate of the world in the hands of others while he does nothing, and showed worry about how the Dandelions would find their way home afterwards.
Initially depressed that Keyblade wielders could do nothing against the impending darkness, Luxu learns from the Master that there is a way to defeat darkness, who notes that it would require extensive planning and many lifetimes to accomplish.
Kingdom Hearts χ Back Cover
Luxu is instructed to meet the Master of Masters in the Foretellers' Chamber, where he is bestowed with a Keyblade containing the Master's own "Gazing Eye". Luxu initially misunderstands that "Gazing Eye" is the name of the Keyblade, but the Master corrects him that it is unnamed, and Luxu names it "No Name" in jest. The Master explains that the Keyblade containing the Eye must be passed from master to apprentice so that the Eye can see events pass throughout the ages, prompting Luxu to realize that the Master's Book of Prophecies was written with the foresight from this process. In order to prevent temporal paradoxes, Luxu is not to receive a copy of the Book like the other apprentices, but is instead tasked with protecting the Black Box. The Master entreats Luxu to abstain from the conflict to come and instead simply observe events. As for the Box, the Master instructs Luxu to never open it or reveal its contents, but at Luxu's insistent questions, he whispers the box's contents to him, shocking and perplexing the boy.
Luxu then sets out to fulfill his role, disappearing as he travels through the Keyblade Graveyard with the Black Box and No Name in hand.
Kingdom Hearts χ
With the Keyblade War approaching, Ava seeks out Luxu to locate the Master in hopes of averting the cataclysmic event with the Master's aid.
Finding Luxu at the outskirts of Daybreak Town, Ava interrogates him, and he explains he is meant to continue on into the future written in the Book of Prophecies and see through the end of the world. Luxu surmises that Ava wants to avoid the Keyblade War and that she had sought him out in order to find the Master, and deems her efforts as useless. Luxu states that the Lost Page is a prophecy that the Foretellers are not aware of and that it is his mission to inherit its secrets. Ava begins to suspect Luxu of being the traitor. Summoning his Keyblade, Luxu proceeds to tell her the truth about the traitor and questions Ava's resolve to stop the Keyblade War when it is unavoidable. Ultimately, Luxu states that even if there was another answer, that would still be the result of the battle and ponders if the Master would rather know how his disciples will guide the keys than the fate of the world. Ava, refusing to believe that the Master would choose them over the world, accuses Luxu to be taking his advantage of the Master's will. Drawing her Keyblade, Ava attacks Luxu, and the clashing of their Keyblades sends a ripple effect throughout Daybreak Town, which tolls the bell that signifies the beginning of the end.
With the No Name Keyblade in his hands, Luxu silently observes the conclusion of the Keyblade War, granting the Master of Masters knowledge of the event.
Kingdom Hearts Union χ
Before Kingdom Hearts Birth by Sleep
Having been instructed by his master to transfer his heart from one vessel to the next until the fated "Dark Master" appeared to reenact the Keyblade War, Luxu's final role is to become an ally of this individual, Xehanort, and aid in his plans in order to continue to observe the future. Luxu’s entire existence within the timeline also provides the new Union leaders a waypoint into the future, using his memories and his No Name Keyblade as a medium.
Like the Master of Masters, Luxu wears a black coat, which completely obscures his features.
Luxu's name is derived from the word luxuria, which means "lust" in Latin.
Contrary to the Master of Masters, Luxu is quiet and reserved. Although he is inquisitive, having asked the Master about the contents of the Black Box, he keeps the promise to never open it and hide it away.
Despite being extremely loyal to his master and the role given to him, Luxu expresses great concern for the future of the world, his fellow Keyblade Masters, the Dandelions, and the seemingly endless war against the darkness. When pressed by the Master of Masters if it bothers him that the best they can do is take a break from the battle against darkness, Luxu expresses his belief that they, as Keyblade wielders, are meant to protect the world from the darkness and is greatly disappointed at the notion that there does not appear to be a way to destroy it once and for all.
When the Master reveals that he does indeed have a plan to destroy the darkness, one that would take lifetimes to achieve, Luxu appears relieved. This indicates that Luxu does not simply want to follow a role if it's not part of a greater goal, namely eradicating the darkness, and is greatly devoted to safeguarding the light and the world.
Perhaps with this greater goal in mind, it further motivated Luxu to do whatever it took to achieve it, including standing by and observing as his comrades commenced the final battle of the original Keyblade War and transferring his heart from vessel to vessel over the course of many years. The secret reports penned by him also show his desire to be reunited with his comrades once more, showing that he still cares for them despite having to play a part in ensuring the original Keyblade War occurred.
All of these characteristics are a stark contrast to the personality of his final vessel, Braig/Xigbar, a laid-back and outspoken seeker of darkness who aided Master Xehanort in causing tragedy to many, indicating that Braig and Xigbar's entire personality was simply a fabrication by Luxu to become a convincing ally for Xehanort and see his role through to the end.
Luxu is a Keyblade Master who is given the No Name by the Master of Masters. Like Xehanort, Luxu has mastered the ability to transfer his heart into others, thereby claiming a new vessel to live on in, discarding the old one; having no Keyblade of his own, Luxu is the only Keyblade Master known able to remove his own heart without one. Unlike Xehanort, Luxu can completely dominate his new host, making the body his own permanently; he revives solely as Braig, while Xehanort regains his original body, separated from Terra.
Through the gazing eye embedded in the No Name Keyblade, Luxu has been allowing the Master of Masters to watch history as it unfolds and record it into the Book of Prophecies, ensuring it happens the way he intends.
Notes and references