Kaeya is an outwardly confident and charming individual with a flair for drama. He is sometimes seen as overly laid-back and even lazy, but he takes his work seriously. He is surprisingly popular among the elderly of Mondstadt, even earning himself the title of "top candidate for grandson-in-law." His charisma and determination have earned him the admiration, respect, and favor of many people in Mondstadt — yet, his love for provoking others has also gained him the exasperation of those same people. Kaeya also enjoys putting people into high-stress situations and challenging their values, which he does to both his enemies and his allies alike. He takes pleasure in seeing the hesitation in his comrades' eyes at the moment just before they dive into battle with him, just as he takes pleasure in the look of fear in his enemies' eyes as they face off against him.
He seems to get a kick out of telling bold-faced lies and convincing others to do his work, but this serves him well in his role in the Knights of Favonius. He is a self-proclaimed "anti-hero with an attitude problem;" as long as everything ends the way he wants, Kaeya does not care about the methods used. Still, according to his informant Vile, he draws the line at working with those who threaten other people's families, believing they deserve to be "hunted down and destroyed."
Despite his extroversion, the Traveler has observed that he appears to struggle with loneliness, though he playfully deflects when confronted about it. He frequently reminds the Traveler that they can talk to him, invites them to spend time with him, insistently offers (sometimes extensive) assistance, and often voices his disappointment whenever the Traveler has to leave, showing his desire to be helpful and aversion to being alone.
It was raining heavily in Mondstadt on the night that Kaeya Alberich received his Vision.
Earlier that day, Crepus Ragnvindr had wielded the power of a Delusion — only to become its victim when it backfired. To set his father free from the unbearable agony, Diluc Ragnvindr took his life.
Kaeya was Diluc's brother by adoption and was always by his side, but on this occasion Kaeya did not partake in the final moments shared between father and son.
The torrential rain that set in on Mondstadt that night seemed to be a sign of the heavens' grief at the passing of Master Crepus.
There was a side to Kaeya that he kept hidden from the world: In truth, he was an agent of Khaenri'ah, placed in Mondstadt to serve their interests. His father had abandoned him in this strange and unknown land to fulfill this mission, and it was Master Crepus and the city of Mondstadt that had welcomed him with open arms when they found him.
If Khaenri'ah and Mondstadt went to war, which side should he support? To whom should he offer his assistance: his birth father, who had ruthlessly abandoned him? Or his adoptive father, who had loved him and raised him?
For the longest time, Kaeya had agonized over these impossible questions, caught between the opposing demands of loyalty and duty, faced with an impossible choice between truth and happiness.
But now, Crepus' death upset this delicate balance. He felt liberated, but also ashamed of how selfishly he was responding. As an adopted son, he should have saved Crepus, but he had arrived moments too late. As a brother, he should have shared in Diluc's grief, and yet as their father lay dying on the ground, he had hung back behind his brother, that ancient plot running through his mind.
Consumed by guilt, Kaeya knocked on Diluc's door. As the rain poured down, the shroud of secrecy was washed away and all lies were revealed. Kaeya had finally come clean.
He had anticipated Diluc's anger. The brothers drew their blades, this time pointing them at each other. Kaeya felt that this was his punishment for a lifetime of lies.
But as the two crossed blades, Kaeya was overcome by the sensation of great elemental power surging through him. For years, he had stayed out of the way in his brother's shadow. But now, for the first time ever, he was facing his brother as his true self.
Bitterly cold and brittle elemental energy burst forth from the tip of his sword to meet Diluc’s [sic] searing flames head-on. The clash of crimson fire and azure ice created a sudden swirl of wind that stunned them both. This was the grim moment at which Kaeya's Vision appeared.
Since that day, Kaeya and Diluc have gone their separate ways. But he never discusses it, just as he never discusses the origin of his Vision.
Though it is a reminder of a hard-fought battle, and the prize that he earned in exchange for revealing the unadulterated truth, Kaeya sees it as a stern reminder that he must live the rest of his life under the heavy burden of lies.
