Chapter Text
"Oh my, oh my... what a coincidence, Master Diluc. Out for a night stroll?"
"...Hmph. Spare me the act."
It was the dead of night, the hour when both good children and bad had long since drifted off to sleep. Within the city walls, there might still be traces of life—drunken stragglers or patrolling knights—but here, far from Mondstadt’s bustling center, Starfell Cliff was wrapped in absolute silence.
Into that silence descended two shadows, quiet as the breeze. Without even glancing at each other, they gazed in the same direction, eyes narrowing in unison.
"Hmm. Just as reported—three Abyss Mages behaving suspiciously... Heh, see, Diluc? The Knights of Favonius aren’t so useless after all, are they?"
"Try saying that after we’ve finished the job. ...Let’s go."
"Yes, yes. Always in such a hurry, aren’t you?"
There was no need for the two of them to exchange intel as they broke into a run. Kaeya knew that Diluc’s famed "network" had already uncovered as much as, if not more than, the Knights' own investigation. And Diluc, in turn, had no doubt that the man beside him, a master of gathering intelligence, wouldn’t be trailing behind him in knowledge either.
Their arrival here, at a suspected Abyss hideout after recent strange activity—it was, in essence, inevitable.
It had been years since they were once likened to twins. And now, they could no longer interact the way they used to. The words they exchanged were sharp, far from honest. Yet... the trust they held for each other was evident, even without words.
Even now, though unspoken, the sight of Diluc running ahead—his back turned in implicit trust—spoke volumes. With a quiet warmth building in his chest, Kaeya matched his pace.
For Diluc, the feeling was mutual. It had always been like this. His younger brother—capable of doing everything on his own—would still come to him, dragging him into things without hesitation. He’d never say it aloud, but... the sound of those familiar footsteps following lightly behind filled him with a joy he couldn’t hide, and a small smile found its way to his lips.
—If only I could express these feelings just a little more.
They both thought it, running in sync. They didn’t dislike the way things were now—but if only their words could be a bit more honest.
If only they could say something like, “I just want to spend time with you,” and invite the other to dinner with no excuse at all... wouldn’t that be wonderful?
And so, while they dashed across the moonlit path, supposedly in pursuit of threats to Mondstadt, the thoughts in their heads were far more personal and far more complicated. Because, after all... Diluc’s birthday was approaching.
—I want to invite my beloved older brother to dinner for his birthday.
This time, Kaeya want to be the one to prepare a special meal, to bring the finest grape juice, to make that day special. He still wonder if he even have the right... but more than guilt, he want to celebrate the man he’s become.
—I want to spend my birthday with my beloved younger brother.
Every year, he shyly says happy birthday. This time, Diluc want to take his hand and keep Kaeya beside him longer. He want to tell him that time with you is the most precious gift of all.
Ironically, their thoughts were almost identical. All that remained was to say them out loud.
But for Diluc and Kaeya, that was the hardest thing in the world.
What if he says no?
What if he looks annoyed?
Maybe I shouldn’t be there on such an important day…
Even if it’s his birthday, is it really okay to monopolize someone so well-loved…?
If the Traveler, Paimon, a certain straightforward scout, or a peculiar nun could peer into their thoughts, they’d likely sigh and tell them, “Just be honest already.” That’s how obvious their mutual hesitation was.
But even the smallest of worries can feel earth-shattering to the person experiencing them. And for Diluc and Kaeya—who protected Mondstadt tirelessly day and night—taking a single step deeper into each other’s hearts was an enormous hurdle.
Even so, no matter how full their minds were of each other, the threats to Mondstadt didn’t wait.
And so, as frustrating as it was that their legs could move so smoothly in battle while their words stumbled in uncertainty... at last, the sound of two sets of footsteps came to a halt.
They had arrived—behind a group of Abyss Mages, huddled around something at the center.
—A single glance.
That was all it took.
Flames engulfed a raised claymore, and in perfect sync, a sword summoned icy spikes. Perfect timing, flawless coordination. Neither ever got in the other’s way. Elemental energy surged in harmony, saturating the battlefield, and then—
“Whoa, hey! Hold up! Attacking out of nowhere—are all humans this hotheaded? Come on, I haven’t even done anything yet!”
In the middle of the scrambling Abyss Mages, a faint glow shimmered at the center where they’d been gathered—and from it emerged a tall, looming figure.
Its voice, mixed with static and inhuman tones, was undeniably foolish—and unmistakably coming from the Abyss creature itself.
“Can’t we try a little diplomacy? Please, put the swords down. I swear I haven’t done anything yet! I was just curious about the distortion in the ley lines! You’re not going to kill a defenseless, curious bystander, right? ...Right?”
"...What the hell is this thing?"
"No idea... Talking to it is a waste of time. If you don’t want to be cut down, how about—"
"Neither! I don’t want either!"
The creature hunched its tall frame, flailing and whining as if begging for its life, successfully throwing Diluc and Kaeya off balance. And while their eyes remained fixed on the bizarre figure, the other Abyss Mages had vanished—scattered or perhaps deliberately released.
The two exchanged a glance.
Should they reduce it to ash here and now—or freeze it and extract information?
Even as they hesitated, the Abyss figure, still grumbling and watching the humans with exaggerated fear, quietly extended one long finger to the ground.
And then, in the next moment—it froze.
"...What’s with it? It just stopped moving."
"Should I burn it?"
"That’s your answer to everything..."
Ignoring their banter, the creature’s focus sharpened.
It felt the ley line’s pulse.
The elemental energy in the air.
The faintest disturbance.
Its curiosity stirred.
And from that, it calculated—the optimal answer.
And then—
“...Hmm? Oh, I see. The disturbance in the ley lines... Hah, is that so? Fascinating, but still...”
—And then, remembering that a perfect test subject just happened to be nearby, it acted immediately.
A breeze stirred, and in the blink of an eye, its sharp fingertip moved—leaving the ground and drifting toward the man who had been watching her from a distance.
Tap. A pointed claw touched Kaeya’s forehead. Yet, nothing flowed into him—nothing happened. It was simply a touch. No pain, no discomfort.
...However, there was a man beside Kaeya who would never permit even that touch.
“...Hmm. The trifling worries of humans are always amusing to peek at, no matter when you do it. Not the kind of troubles I usually care about, though.”
“Get your hand off Kaeya!”
“Oh dear, how scary. …Well then, maybe I’ll go with you instead. I'd rather not be burned.”
“Hah—”
With a lazy wave of its hand, the Abyssal Spellcaster muttered something under its breath—and this time, reached its sharp finger toward Diluc, who had stepped in front of Kaeya to protect him.
—In that instant, the surrounding light flared so brightly it was impossible to keep one's eyes open. Not only the spellcaster, but even Diluc—who had been standing right in front of him—disappeared from Kaeya's view.
Fear. Panic. Rage. Any of these could be the correct name for the emotion that surged in Kaeya’s chest. Instinctively, he reached out his hand and stepped into the light.
“Diluc!”
“Don’t panic, young one. It’ll only last for a day. By this time tomorrow, everything will be back to normal. Just one day—but maybe after witnessing the potential of your future selves, those petty worries of yours will vanish, hm?”
The root of all evil was still rambling on, but Kaeya no longer heard a word of that static-laced voice. Whatever it said, whatever it was thinking—it didn’t matter in the slightest. The only truth was this: it had harmed Diluc, right before his eyes.
Gathering elemental energy, he formed icy shards—his killing intent, clear and sharp as ice, concentrated at the tip of his blade. But in that divine light, the target danced away with infuriating grace, evading his strike with ease.
“Mm, I did a good deed today, didn’t I? Farewell, little lost lambs! May I never meet such violent humans as you two again—I truly wish it from the bottom of my heart!”
Jesting all the way, the Abyssal Spellcaster proved at least one thing: it was incredibly quick to flee. By the time the light faded and the air warped with spatial distortion, even the sharp claws were nowhere to be seen.
—Under normal circumstances, Kaeya would have done whatever it took—grabbing hold of the spellcaster's fading form, if need be—to pursue the target. Because it dared to lay hands on Diluc Ragnvindr. It harmed the only family Kaeya had, right in front of his eyes. That alone was reason enough to chase it to the ends of the earth, to freeze it in place, and shatter it to pieces.
—However, now Kaeya had a reason he couldn’t do that.
And of course... that reason was Diluc Ragnvindr.
A breeze swept through again, passing between Kaeya—no, between the two of them.
Slightly longer red hair. The familiar scents of grapes and smoke. Muscular arms that could easily wield a claymore one-handed. And though the face looked no different at first glance… there was one unmistakable difference.
His eyes. The emotions in those eyes. The weight they carried. All of it… was different.
Far more than the fine lines that had begun to form at the corners of his eyes, the difference was clear.
—He’s different. And yet... because Kaeya Alberich is Kaeya Alberich, he knew it instinctively.
The man before him was the most important person in his life.
The man he had just thought lost forever.
“...Diluc?”
“Ah, that’s right. I remember now. It was this moment... I’d forgotten it until now.”
The voice that answered was slightly deeper than the one Kaeya knew so well. Rich and mellow—like wine aged for many years. A voice sweet and warm, from someone who had tasted life’s bitterness and sweetness alike, and had come to understand what truly mattered.
The man glanced briefly around them, then smiled knowingly, as if he already understood everything.
That smile, too, was unfamiliar to Kaeya.
“Good evening, Kaeya. Haha… you look so young. How nostalgic.”
With a gentle smile, the man reached out, his gaze softened by something Kaeya didn’t yet understand. He touched Kaeya’s hair, then his cheek with affection. His hand, trembling slightly, touched Kaeya’s frozen palm with warmth, stroking it gently before speaking again, voice filled with the same unknowable emotion.
“I haven’t introduced myself, have I? I’m… well, from your perspective, I’m Diluc Ragnvindr—exactly ten years from now. I’ll be in your care, just for today.”
—And with that, Diluc Ragnvindr gave a soft, loving smile to the dumbstruck man before him, whose mouth hung open in disbelief.