Prologue: The Gremory Mansion
To many, the Gremory mansion was considered the finest place to serve—if you were a low-class demon whose greatest aspiration in life was to work directly under one of the 72 pillars of the Ars Goetia.
And yet, the truth was… the place was completely boring and quiet most of the time. The only sounds came from the servants going about their daily routines, always at the same time of day.
Sometimes unnecessarily so—silverware, velvet curtains, stained glass windows… none of it really needed to be cleaned or polished every single day without fail. After all, they were rarely even used. Though, it was somewhat understandable that the family portraits were dusted daily. For some reason very few could truly grasp, demons had a habit of honoring their ancestors.
Still, beyond all the grandeur of the mansion, there was a secret hiding in plain sight… or rather, a child that very few within—or outside—the clan ever bothered to notice.
Naruto Gremory, none other than the third son of the current Gremory patriarch. And truth be told, many saw him as a rather hard-to-read boy. His behavior, his attitude—so different from his older siblings—and the fact that everyone knew Venelana wasn't his mother.
If anyone ever actually asked about him, most of the servants wouldn't even know what to say, simply because they didn't know he existed. Those who did know gave different answers: some said he was just another Gremory; others that he was a backup in case something happened to Rias-sama; and a few whispered he was just a lucky bastard.
But every single one of those dismissive comments missed the truth about the boy. Not surprising, considering how conveniently everyone ignored Rias's flaws just because she was born with the "Power of Destruction."
After all, there's a fundamental difference between destroying things and knowing how to destroy them.
Most of the staff didn't understand that simple truth. Naruto figured it out when he was five—after watching his sister get praised for her temper tantrums, praised for losing control of her power.
Idiots… no, they were morons. Morons blind to the fact that Rias was destined to be nothing more than a stain on the Gremory name.
And Naruto had no doubt that if Grandma Runeas were still alive, she'd probably have disinherited Rias… and Zeoticus too, for letting her act that way.
Honestly, that idea was pretty appealing, and something worth looking into. After all, who better to slap some sense into a sister with stupid ideals than the founder of your clan?
When that thought crossed his mind, his deep blue eyes—bright like stars—shone just a little more intensely than usual.
But setting aside those comforting little bedtime thoughts, Naruto, barely ten years old, had just been stopped halfway to his room by his older brother, Sirzechs Lucifer, who—in his honest and absolutely unflattering opinion—looked even more like an idiot than usual.
An idiot and clearly nervous, which made it obvious that he'd done something monumentally stupid and now needed his little brother's advice to get out of it… which was both funny and sad on multiple levels.
Even so, Naruto wasn't going to make it easy on him. He simply stared at him with his bright blue eyes—but with a coldness no ten-year-old should be capable of.
Sirzechs, for his part, couldn't help but fidget under the stare. His brother's eyes—though confirmed by several demons to just be "unusually bright"—always felt a bit terrifying to him. Not because he feared a child, but because the glow was completely unnatural, even for a demon.
"Who is she?" Naruto asked at last, with the tone Sirzechs—and most of the mansion staff—had learned to interpret as his "curious" tone.
Which was extremely hard to pick out, given the apathy and monotony in his voice whenever he spoke.
To be fair, Sirzechs sometimes wondered if being born to one of their father's mistresses and raised with no nannies—since they all chose to look after Rias-chan instead—had caused some kind of trauma…
Nah, his little brother was probably just weird. According to Ajuka, strong demons tended to have weird personalities from childhood anyway.
Now, as for the girl who'd caught the interest of Naruto Gremory: she was a young blonde—not quite platinum, but not golden like a Phoenix either.
She had pretty, amber-colored eyes that were currently fixed on the floor like it was the most fascinating thing in the world, clearly trying to avoid the kid's penetrating gaze.
She wore a stained, tattered kimono, and—though he'd never admit it out loud—had two lovely, snowy-white tails twitching nervously behind her. And of course, he also wouldn't admit that he kind of wanted to pet them.
He had a reputation as the cold kid to uphold, after all.
"I got her to be the first member of your noble house," Sirzechs said, with a painfully forced smile that fooled absolutely no one. Least of all Naruto.
His older brother's brand of joy was the kind you just can't fake… because it's the joy of a moron.
Also, his voice cracked pretty badly when he said it.
"Idiot," the younger Gremory couldn't help thinking, maintaining the best poker face in his arsenal as he stared back at his brother.
Then he simply chose to spend his time on something more important: trying to remember what exactly Sirzechs had done this time to become even more of an idiot than he already was.
I mean, Amaterasu literally threatened to burn his ashes if he ever set foot in Japan again—and knowing the temperament of the goddess of the sun and the universe, Naruto had no doubt she'd carry out that threat happily while giggling like a little girl roasting marshmallows.
And thinking about that goddess was what made Naruto finally realize what was going on—not because he saw it firsthand, but because apparently all four Maou had decided to use him as their unofficial therapist.
Well, semi-official, maybe. They all paid him in weird stuff. And not "rare" as in hard-to-find, just… weird.
Serafall literally paid him with signed photos of herself in magical girl costumes. For the love of Lucifer.
But anyway, he was rambling.
The point was, according to what Serafall said in their last little "session," Amaterasu had been so furious that Sirzechs had ordered the Nekoshou massacre, she'd screamed that—on top of all that—he'd forgotten he didn't have one sister but two, and that he'd doomed all of the Underworld for a spoiled brat.
"What kind of thought process leads to this?" Naruto couldn't help but wonder.
After all, no normal person would hear "you forgot your little sibling and now there's a threat of total war with Takamagahara" and think, I should make it up to him somehow.
Then again, Sirzechs had a habit of jumping from point A to point Z without going through the rest of the alphabet first.
"Please tell me he didn't kill your family to get you," Naruto asked the girl. Honestly, he was too young to be making enemies of a goddess who literally cast the world into three days of darkness just because her brother killed her horse.
"Uhm… I was already an orphan when he found me," the girl said shyly, still avoiding Naruto's eyes.
That actually made sense. Kitsune were rare, and one with two tails at such a young age—without being a direct descendant of a high-tailed kitsune—was extremely rare.
As far as he knew, Princess Kunou had only been born with one tail.
"You need a bath and clean clothes," Naruto said at last.
Now that his fears of being blacklisted by the sun goddess were eased, he could finally appreciate his brother's gift.
Of course, that didn't mean he'd stop seeing Sirzechs as a complete idiot… but hey, it was a nice gift.
The girl had to cough into her hand to build up some courage, although the deep blush on her cheeks only made her look even cuter in Naruto's eyes.
Her hazel eyes, trembling with insecurity, gave her such an adorably vulnerable aura that—if it weren't for his iron will—he might've been tempted to hug her until she popped.
"Nice to meet you, I'm Natsumi. It's a pleasure to meet you, I hope I'll be a good member of your noble house," she said all in one breath—miraculously without biting her tongue—while giving a deep bow… well, almost; she didn't kneel, just lowered her head.
That gesture, aside from making Naruto genuinely smile at how adorable she looked, also gave him a clear view of her rear—err, her tails, which were still nervously swaying.
To have two tails at ten years old, she must've had immense potential. He wasn't sure of her lineage, but kitsune were rare, so there weren't many lines to investigate.
Something he would… look into. Eventually. Sometime next year.
Alright, whenever he remembered and had the time.
The topic, while important, wouldn't really offer much beyond a few powers she might have. And anyway, it was always better to discover capabilities firsthand than to trust ancient records.
Putting that aside, Naruto followed his instincts. He dug into his pocket for a few seconds and pulled out a chess piece—hand-carved from ebony wood, adorned with touches of ivory, and embedded with a small red gemstone that served as its power source.
Sirzechs, who had been quietly observing the scene, widened his eyes in mild surprise.
He had no idea why his brother would choose to use something as significant as the Queen piece on a kitsune of unknown lineage.
Naruto, of course, paid his brother no attention, fully focused on explaining in detail what Natsumi had to do to make the reincarnation process as painless as possible.
A process the Demon King himself listened to carefully—making a mental note to ask Ajuka whether what his brother was saying was true or not.
With preparations complete, Naruto began chanting a reincarnation ritual—one quite different from the one Sirzechs was used to hearing.
And to be honest, he was pretty shocked by how fluently his little brother spoke ancient Sumerian.
The whole thing didn't last more than ten minutes before the Queen piece's power was fully absorbed into the girl's body, merging with her essence and flooding her veins with a wave of energy unlike anything she'd ever felt before.
A surge of heat followed, intense but not unpleasant.
When it was over, Naruto helped her stand up, then gave his brother a subtle nod and gestured for Natsumi to follow him straight to his room—or as Rias liked to call it: "his mad scientist's cave."
One of the few places in the mansion where he could be free of servants—who had learned the hard way not to bother him after one experiment turned a servant into a mouse…
And then Latia's cat ate the mouse.
Once they crossed the threshold, Natsumi felt like she'd stepped into another world.
The place was clean, no doubt, but it smelled of old paper, mysterious substances she wasn't sure she wanted to identify, and… was that strawberry cake?
Setting aside the scent, her eyes took in the controlled chaos around her.
Rows of bookshelves packed with tomes on various topics and notebooks—probably filled with notes on the dozens of projects her new master was working on. Tables covered in scrolls, notes, and diagrams she couldn't make heads or tails of.
And several artifacts that looked so delicate and expensive she made a silent promise never to touch them.
She was legally a slave now—and she definitely didn't want to add "indebted to her master" to the list. No thanks.
So with that in mind, she focused on the one place that looked somewhat safe: the wooden desk that was noticeably more organized than the rest of the room.
Not because it was free of clutter—oh no, it was still covered in scribbled notes, complex diagrams, and trinkets that reeked of alchemy—but because it seemed like the only place where breaking something wouldn't cost her a lifetime of servitude.
Being a fox spirit—naturally curious—she walked over and examined the desk.
Her master's handwriting, she noted, was just as chaotic as his room.
She figured she could eventually decipher it, but wasn't sure if he'd appreciate her snooping, so she left it alone for now.
Then, something shiny caught her attention.
She turned her head and saw a photo in a silver frame.
In it was Naruto, alongside a blonde girl with a mischievous gleam in her eyes who had clearly forced him into a tea party.
"That's Latia," Naruto's voice made her squeak a little in surprise—she hadn't expected him to talk to her.
Then again, she had been poking around in his room.
Naruto found her reaction insanely cute, but didn't comment on it.
"Anyway, she's my master's niece. A very good friend."
"Right now, I was just studying the properties of various magical metals."
Natsumi blinked at him in confusion. That at least explained the strong alchemical scent.
Well, as long as he wasn't trying to make a philosopher's stone, she'd be happy to help however she could.
"Wanna help?" he asked, offering her a pair of safety goggles.
She blushed again, realizing either he could read her thoughts—or they were just that obvious.
Still, she took the goggles, quietly enjoying (though she'd never admit it) the slight tingle she felt when their fingers touched.