Kaeya Alberich is an adopted son to the Ragnvindr Family, the renowned wine tycoon.
It has been a long time since he last called Diluc Ragnvindr "brother."
Kaeya currently serves as the Cavalry Captain of the Knights of Favonius, and is trusted by Jean.
Kaeya is often the one wrapping things up in every incident that occurs in Mondstadt's vicinity.

It is a curious fact that your best chance of finding Kaeya is not by visiting the Knights' headquarters, but by frequenting the taverns at night.
Kaeya is often found sitting at the bar, gossiping with the city folk, and sipping the famed Mondstadt beverage, Death After Noon.
He is surprisingly popular among the elderly of Mondstadt, even earning himself the title of "top candidate for grandson-in-law."
It's hard to imagine someone as mischievous, amiable, and wine-loving as Kaeya being the Cavalry Captain of the Knights of Favonius.
Hunters and bandits alike are often among Kaeya's drinking buddies. As wary of him as they may initially be, all are ultimately disarmed by his smooth talking, and end up telling him everything he wants to know.
Depending on what they then make privy to Kaeya, their night may turn into an uncontrollable nightmare or remain one of harmless banter.
"Everyone's got a secret, but not everyone knows what to do with it."
Says Kaeya, with his usual arrogant smirk.

"Justice is not an absolute principle, but is the result of striking that fine balance between strength and strategy. As for the details of how it's done... Don't worry yourself too much about that."
Kaeya once said these words in front of Grand Master Varka.
As long as everything falls into place the way he expects in the end, Kaeya doesn't care all that much about the means.
This cavalier attitude is what defines his character.
Not so unlike Death After Noon's wild and explosive taste, one might add.
However, his reckless approach to things is not uncontroversial.
Once, in order to force a bandit leader into facing him directly, Kaeya triggered the Ruin Guard at an ancient ruin to cut his opponent off, putting his own men at risk in the process.
It's times like these when even Jean, who puts a lot of trust in Kaeya, finds herself shaking her head in disapproval.
Not that this bothers Kaeya, of course. On the contrary, he actually enjoys putting people into the difficult position of making tough decisions.
He takes pleasure in seeing the hesitation in his comrades' eyes in 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.

The flourishing winery business in Mondstadt has been a great source of prosperity in the region over the years. This prosperity often entices greedy bandits and monsters to the area.
They are a motley bunch who hide in the shadows, and their backgrounds, motives, and allegiances are varied and complex.
Kaeya battles against this threat to Mondstadt not only with his sword, but also with his smarts and his wit.
A young knight once dedicated years of his life to studying threats in and around Mondstadt, and reached an astounding conclusion:
When Death After Noon is out of season due to lack of supply, the number of reported incidents inside and outside the city show a drastic decrease, and this remains the case until Death After Noon returns to the market...
The young knight showed his findings to Cavalry Captain Kaeya in hopes of getting some advice from him.
"Interesting. I'll look into it." Kaeya answered, with a wry smirk on his face.

Generally speaking, Kaeya is an easy person to have a conversation with. The only topic that you will never hear him discuss is his past.
Even when the Grand Master demanded information on his background, Kaeya skirted around the issue and gave only vague answers devoid of details.
"One afternoon near the end of summer a decade ago, my father and I passed by the Dawn Winery."
"'I'll go get us some grape juice for the road,' he said, but he never came back."
"If Master Crepus hadn't taken me in, I doubt I'd have made it through the storm that night."
This matter-of-fact description hides a carefully constructed lie.
Kaeya has never once spoken the truth about what happened that afternoon:
"This is your chance. You are our last hope."
Kaeya's father squeezed his son's lean shoulders as he spoke, seemingly looking right through Kaeya to some place far beyond.
On the other side of the horizon sat their distant homeland of Khaenri'ah.
Kaeya would never forget the look of both hope and hatred in his father's eyes as he uttered those words.

Many citizens still remember the two most eye-catching young gentlemen in all of Mondstadt a few years ago.
One of them was the dapper Diluc, an elegant swordsman who always had a warm smile and a confident posture.
The other was the eccentric Kaeya. He was Diluc's friend, supporter, and sounding board, ensuring he got through every challenge he faced smoothly.
They were almost like twins, knowing each other's thoughts and intentions without a word, protecting Mondstadt in both light and dark.
...Until that fateful day, now ingrained deep in Kaeya's memory, when the convoy that Diluc was escorting was attacked by a huge monster.
It was the first and only time that Kaeya failed in his duty.
By the time Kaeya finally reached Diluc, it was all over.
The power their father had used to successfully fend off the attack backfired, taking their father's life.
Both Kaeya and Diluc were shocked by what they had witnessed, losing the calm composure a knight should retain.
"Even someone like Master Crepus would submit to such a dangerous and evil power..."
Sinister thoughts flashed through Kaeya's mind, and he simply smirked:
"This world is truly... fascinating."
All while their father lay dead in a pool of his own blood. It was on that night that the two sons' paths diverged.

Between the pages of "The Adventures of Angelos," you find a list of names written on a sheet of official Knights of Favonius letterhead paper.
It meticulously records the details of bandits in the city and further afield, as well as mercenaries and mid-to-senior-level Treasure Hoarder members, listing for each entry a name, position, area of activity, and personal profile.
A dozen or so names are circled, with a note in the margin saying "Otherwise, things would get too boring."
When questioned about it, Kaeya's response is "I suppose I must have gotten drunk and started scribbling nonsense."
Your gut feeling is that Kaeya purposely let you see this list, but you have no way of proving it.

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 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.