The next morning, Uchiha Hikari woke up early, thanks to her internal clock. After washing up and grabbing breakfast, she joined Karin and Kimimaro at their invitation to watch their ninjutsu practice on a nearby training field.
Both kids had solid talent for training.
Kimimaro, in particular, stood out. Two years older than Karin and already skilled in taijutsu, he'd been close to chunin-level even when locked in the Kaguya clan's dungeon. Now, after months of Orochimaru's focused tutoring in the Sound Village, his progress was remarkable.
"What do you think, Es?" Hikari asked, glancing at the battle-hardened woman beside her.
"…Not bad," Esdeath replied, arms crossed casually. "They're a bit weak and their moves lack sharpness, but for their age, they're decent enough. Together, they could probably take down a regular Dangerous Species."
"Uh…" Hikari blinked.
So, the benchmark for "good" was whether they could hunt a Dangerous Species?
Fair enough. Esdeath, at their age, had already taken down most of the Dangerous and Super Dangerous Species in the Empire's northern territories. Compared to her, not just Karin and Kimimaro, but even Hashirama Senju or Madara Uchiha at that age probably wouldn't measure up.
Meanwhile, Karin and Kimimaro finished their spar, panting as they jogged back. Karin looked up at Hikari with eager eyes. "How'd we do, Big Sis Hikari?"
"Not bad at all," Hikari said warmly, bending down to praise them and correct a few bad habits. Her gaze shifted to Kimimaro—his shirt was riddled with holes from his Shikotsumyaku bone spikes, looking like some avant-garde fashion statement. She wondered how many more wears it could handle.
Maybe I should make him some soft armor from East Sea Cloud Dragon fur, she thought. Bursting his clothes every time he uses his kekkei genkai isn't just impractical—it's wasteful.
"By the way, has Orochimaru been checking up on you lately, Kimimaro?" she asked.
"Yes," Kimimaro nodded obediently. "Every two weeks, Teacher arranges a full physical. When he's not around, Sister Nonou takes over. He also prescribed some medicine for me to take daily."
"Oh? What kind?"
"Green ginger, white atractylodes, red flame flower, frostweed…"
"?" Hikari's brow furrowed. What are those?
Seeing her confusion, Karin chimed in, explaining that these were herbs tied to bone development, some used by the Kaguya clan since the Warring States era. Orochimaru had acquired the recipe through his connections and tweaked it for better results. He was also experimenting with "demon" and "dragon king" cell extracts to boost Kimimaro's self-healing, hoping to counter his kekkei genkai's bloodline disease. But that research was still in early stages and needed extensive testing before it could be used on him.
"Got it," Hikari nodded, planning to ask Orochimaru for the data later to share with Dr. Gero. Combining their efforts might speed things up.
For now, though, Orochimaru was likely busy with the clinical trial plans, so Hikari decided not to bother him. After encouraging Karin and Kimimaro, she and Esdeath wandered out of the village.
They strolled through the main street, left the Sound Village, and followed a winding path to a small hill a few kilometers away. There, Hikari stopped, found a clean rock to sit on, and stretched lazily. The motion accentuated the soft curve of her waist, her T-shirt riding up to reveal a glimpse of toned abs that caught the eye.
"Juice or cola, Es?" Hikari asked, pulling out both from a Capsule.
Esdeath took the juice, and Hikari popped open the cola, sipping it while enjoying the cool mountain breeze. Then, from a sealed scroll, she released Nakime.
"…Lady Hikari," Nakime said, still clutching her biwa. After a quick glance around, she bowed respectfully.
"Mm," Hikari responded, taking another sip of cola before eyeing the long-haired demon. "Let's see if your Infinity Castle works properly here."
"…Please wait a moment," Nakime replied, plucking her biwa strings.
In an instant, her figure vanished before Hikari and Esdeath.
Seven or eight seconds later, she reappeared.
"Hm?" Esdeath's casual expression sharpened with interest. "This demon's ability—it's like a spatial technique similar to 'Shangri-La,' isn't it? Pretty intriguing."
"Definitely," Hikari agreed, observing more closely.
To her, Nakime's entry and exit from the Infinity Castle wasn't quite true teleportation. It required the act of plucking the biwa strings, with a brief wind-up of a few tenths of a second. For most people, that was negligible—too fast to react to. But for someone with exceptional reflexes and perception, it might be enough to strike her down the moment she appeared or disappeared.
Not that many could pull that off.
Plus, Nakime could reappear in a different location, potentially dozens of miles away. If she had Muzan's shameless personality and chose to hide in the Infinity Castle for decades after entering, even Hikari might struggle to track her down—the Yasakani no Magatama's connection didn't work across dimensions.
"Say, if we kept feeding Nakime Muzan's blood, could we push her Blood Demon Art further?" Hikari mused, then spoke softly. "Pull me in. I want to see it."
"Alright," Nakime nodded.
With a gentle strum of the biwa, her figure vanished again. Hikari's vision blurred, and when it cleared, she stood in a vast, sepia-toned space, her feet on a checkered floor.
The Infinity Castle.
She'd seen it countless times in the Demon Slayer anime, but this was her first time inside.
All directions—forward, backward, left, right, up, down—stretched endlessly into a black void, dotted with wooden rooms linked like building blocks. Some were fixed, others moved like floating elevators. The visual effect was striking, to say the least.
Hikari shaded her eyes, scanning the expanse before focusing on Nakime, who knelt nearby with her biwa, awaiting orders.
"Nakime, how big is this place?"
"…I don't know," Nakime replied.
"Huh?" Hikari's forehead sprouted a question mark. "Your own Blood Demon Art, and you don't know?"
"…I've never measured it."
"…"
After confirming Nakime wasn't lying, Hikari formed hand signs and summoned seven or eight shadow clones. They took off using the Flight Technique, scattering in different directions to physically measure the Infinity Castle's scale.
Her main body stayed put, stomping the floor and peering over the room's edge into the pitch-black abyss below.
"I recall you can freely manipulate the terrain here, right?"
"Yes," Nakime answered promptly. "The Infinity Castle is shaped around me, so I can alter its structure based on my perception. But I can only reshape what's already here—I can't create things from nothing."
"So the lab equipment Muzan used was brought in from outside?"
"…Yes."
Nakime plucked her biwa again. With a flicker of light and shadow, the door to the next room opened and closed, its contents shifting instantly. Tables, chairs, bookshelves, beakers, test tubes, and scales appeared as if by magic.
"This is the room Lord Muzan once used. Please take a look," Nakime said.
Hikari stepped inside, glanced at the books on the shelves, and quickly turned back. Muzan's rotten personality made his old haunt feel… off-putting.
Still, if Muzan could build a lab here, Hikari could turn it into a secret base.
"If you can reshape the space, making a villa or even a castle shouldn't be an issue, right?" she mused. "This could be a bedroom, that a study, a game room, a theater… Bring in some sofas, wardrobes, and gaming consoles from outside, spruce it up, and it's a proper base. Hmm… could we move a gravity training room in here?"
She asked Nakime about restrictions on bringing items in.
"Well…" Nakime hesitated, her words vague. "I'm not sure how large or heavy objects can be. I've only brought in furniture and supplies for Lord Muzan before… but as long as it's not too extreme, it should be fine."
"Is that so…" Hikari wondered. Would a kilometer-long East Sea Cloud Dragon count as extreme? What if it was shrunk a hundred times with a Mini Band?
She'd have to run some tests later.
Next, Hikari asked about Nakime's "eyeball creation" ability. Nakime explained that the eyeballs were made from her flesh, linked to her optic nerves. She could send them in and out of the Infinity Castle via her biwa, transmitting what they saw back to her.
As for range, in the Demon Slayer world, she could monitor half of Kanto—about a few dozen miles. In the original story, she'd used this to locate the Demon Slayer Corps' headquarters and most of its members' homes. While the Ubuyashiki family's leak helped, her ability was still impressive. Beyond that range, there'd be a delay in the visuals.
Her teleportation range was even greater—hundreds of miles for precise drops. But sending someone from Japan to China or Europe? That was pushing it. She could try, but she'd lose control over the destination, essentially tossing them blindly. They might land in a volcano and get a lava bath.
"Got it," Hikari said, estimating the scale.
The Naruto world's main continent, while limited to the Five Great Nations, was still vast. Nakime's real-time surveillance range covered roughly the Land of Rice Fields, with precise teleportation spanning about half the Land of Fire.
"Not bad," Hikari concluded. Given the lower power level of the Demon Slayer world, Nakime was already an anomaly. Hikari didn't expect more. With "Shangri-La" already handling teleportation, Nakime's ability was a nice bonus, especially her surveillance, which was like an upgraded version of Kagura's Mind's Eye. If Muzan's tissue research progressed, her Blood Demon Art might be enhanced further, expanding its range.
For now, Hikari described her vision for a "villa-style castle" and guided Nakime to shape it with her Blood Demon Art.
It felt a bit like playing Minecraft or stacking toy blocks.
After nearly an hour of tweaking, a four-story castle prototype took shape. Hikari then unloaded some miscellaneous items from her Capsules—priceless antiques and paintings from Minister Honest and the Red Ribbon Army, plus manga, books, and DVDs—placing them in the villa to clear her inventory.
The process took a while.
Just then, her shadow clones, sent to explore the castle's boundaries, started returning.
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