This wasn't the first time Uchiha Hikari had brought up wanting to learn the "Yin Seal."
The last time was late last year, when Tsunade returned to the village and gave Danzo a thrashing. Back then, Tsunade was in a slump, indifferent to everything around her, and Hikari was just starting to experiment with the "Yasaka no Magatama," a technique to rewrite others' wills. Not confident in her control, she didn't dare use Tsunade as a test subject, so the plan was shelved.
Until now—
"…If you're really set on learning the Yin Seal, I can teach you," Tsunade said after a long pause, taking a deep breath and speaking softly. "But I have one condition: no matter what happens, you cannot use this jutsu against Konoha's ninja. Especially not against Shizune."
"No problem," Hikari replied without hesitation.
For her, the Yin Seal was just icing on the cake. Besides, it wasn't an offensive technique—it was for storing chakra, a backup for emergencies. If she ever had to fight Konoha's ninja… well, she doubted anyone could push her to the point of needing the Yin Seal's extra chakra reserves.
Unless it's Might Guy with all Eight Gates open, she mused. That could be a real threat. But even then, the Yin Seal—or even Fire Thunder God—might not cut it. Better to just hop to another world, wait out his ultimate move, and come back when it's safe.
Tsunade knew this too, deep down. Her condition was more for peace of mind than anything else.
Hikari pushed further. "Besides the Yin Seal, I'm kinda curious about a few other techniques… How about 'Super Strength'? Willing to part with that? Or maybe the 'Ninja Art: Mitotic Regeneration' or the contract scroll for the Shikkotsu Forest? I'm good for it, even if the price is steep."
Tsunade: "…"
After some haggling, Hikari ended up paying 18 million ryo for lifetime rights to the Yin Seal, Super Strength, and Mitotic Regeneration, plus a month of one-on-one training with Tsunade herself. As for the Shikkotsu Forest scroll… Tsunade flat-out refused to sell, and Hikari had to let it go.
Not that she could've signed it anyway—she already had a summoning contract with the Ryuchi Cave. Sure, a ninja could theoretically bond with multiple summoning beasts, but the three sacred grounds were a different story. They weren't likely to share a contractor, and a misstep could get her rejected by both or even have her contract canceled outright.
Still, Hikari couldn't help but wonder: What if someone like Eriri or Esdeath signed with Shikkotsu Forest? If it was just raw senjutsu pulling from natural energy, even someone from another world should be able to learn it, right?
She tucked that thought away, planning to ask the White Snake Sage at Ryuchi Cave when she got the chance. With her current strength, she figured she could hold her own in a conversation with the sage.
Tsunade took a few days to recover from the mental strain. During that time, she explained the Yin Seal to Hikari through verbal instruction.
As the name suggests, the Yin Seal is a sealing jutsu, and a rare medical one at that. Its core idea is to fine-tune the body's chakra pathways to create a "reservoir" for storing chakra bit by bit over time. When the moment calls for it, a specific technique releases the seal, unleashing a massive burst of chakra for a huge boost in combat power.
Tsunade had refined the technique further. Her version used a steady trickle of chakra to form a special circuit in the body, constantly repairing and regulating bodily functions to maintain eternal youth. But this upgrade came at a cost: the improved Yin Seal was way harder to master.
In the original story, even Shizune, who'd studied under Tsunade for years, couldn't learn it due to her limitations. Sakura Haruno, a prodigy among regular ninja, took nearly three years to get it down.
As for Hikari… she could tell just from Tsunade's explanation that this was no walk in the park. If regular sealing jutsu were a difficulty of 1, the Four Symbols Seal might be a 3, but the Yin Seal? That was a 5, maybe even a 7.
For a moment, it felt like she was back in her old college days, sitting through a lecture on advanced calculus. She could follow along, but it took focus.
But when Hikari actually tried channeling her chakra according to Tsunade's instructions, things took a surprising turn.
"Huh?" she muttered. "Why does this feel… kinda easy? Way easier than I expected."
Before she could double-check, Tsunade's jaw dropped, her eyes wide with disbelief. "You…"
"What's wrong?"
"…Go look in a mirror."
Hikari hesitated, then walked over to a mirror, admiring her fair, delicate features for a moment. Then she saw it: right in the center of her forehead, a faint purple diamond-shaped mark had appeared.
The telltale sign of a fully formed Yin Seal.
"Not bad, pretty stylish," Hikari said, grinning. "Would've been cool to pick the shape, though."
Her next thought: Wait, am I some kind of sealing jutsu prodigy?
But she quickly pieced it together. This wasn't just talent—it was her body's unique recovery ability, a gift from her wish to Shenron long ago. Her insane regeneration had been constantly fine-tuning her body for the past year, doing the same kind of work the Yin Seal required. It was a different method, but the result was the same—she'd skipped the hardest, most time-consuming part of the process.
Tsunade, of course, had no idea about any of this. After checking to confirm Hikari had actually mastered the Yin Seal, the forty-something blonde stood there, mouth agape, questioning reality.
"No wonder she's the Uchiha clan's ancestral grandma," Tsunade muttered. "That kind of talent is just…"
"Too bad she's an Uchiha," she thought privately. If a genius like this had been born into the Senju clan—maybe even to Nawaki—he might not have…
Tsunade shook her head, snapping out of it. "I'm impressed, but don't get cocky," she said, clearing her throat. "Building the chakra circuit is just the first step. What really matters is the size of your 'reservoir.' The human body's chakra pathways have limits, and you can only expand them so much before risking damage. Unless you've got a one-in-a-million physique like my grandfather, Hashirama Senju…"
Hikari blinked. She knew all about Hashirama's freakish vitality—Tsunade's prized Mitotic Regeneration was basically his passive ability. But Hikari? Her own body was even stronger than his. Hashirama could reattach limbs, sure, but regrowing them from nothing? That was her domain.
If chakra pathway capacity scaled with recovery ability… then yeah, she might just be a Yin Seal prodigy after all.
Since she'd paid for a month of personal training, Hikari decided to take her time mastering the Yin Seal before moving on to Mitotic Regeneration and Super Strength.
Meanwhile, the situation in the Land of Demons was starting to shift.
That evening, as the sun set in a blood-red glow, the capital of the Land of Demons stood solemn. In the grand hall at its heart, a woman in a white robe and golden crown sat on an elevated throne, listening to her subordinate's report.
"…Is it confirmed?" she asked.
"Yes, Lady Miroku," the general replied. "According to our scouts, the seal on the 'Moryo' has indeed been broken, likely by the Yellow Springs Cult. The garrison at Ogutani Castle has gone silent, and General Takanotsume is pulling troops from other regions to reinforce, but…"
He trailed off, but the implication was clear.
"Things don't look good, do they?" Miroku sighed. "This day was inevitable. Moryo's existence was bound to draw the attention of ambitious schemers. That it's happening now is actually a silver lining—at least I still have the strength to suppress it. Ryunosuke, have the five great nations responded to our requests for aid?"
"Yes," Ryunosuke nodded. "Konoha and Suna have sent ninja. Iwa flat-out refused, and we're still waiting to hear from the other two."
He paused, as if remembering something. "Oh, and one more thing. After checking border records, we found something interesting… One of Konoha's legendary Sannin, Hashirama Senju's granddaughter, the unmatched medic-nin Tsunade, might already be in the Land of Demons!"
Miroku raised an eyebrow. "Oh? Where is she now?"
Later that night, in the western reaches of the Land of Demons, a squad of well-equipped cavalry galloped along an ancient stone road, arriving at the mountain-ringed Ogutani Castle.
"We're here," the captain said, dismounting and gripping his sword. "Spread out and search the area. Stay sharp—something feels off."
The Land of Demons, a small nation north of the main continent, wasn't as prosperous as the five great nations. Ogutani Castle was no bustling metropolis, but it was home to thousands. Yet now, not a single guard or civilian was in sight. The streets were lined with dilapidated houses, their long shadows stretching under the fading sunset, giving the city the eerie feel of an abandoned graveyard. Even the seasoned soldiers felt a creeping unease.
Suddenly, one of the cavalry spotted something—a pool of blood. Or rather, a gruesome pile of crushed flesh and bone fragments, as if dozens of people had been pulverized into a single, reeking mass under immense pressure.
Another soldier perked up, listening intently. "Hey, do you hear that?"
"What?"
A faint rustling sound broke the silence.
In that moment, everyone heard it—and felt an unsettling, heart-pounding power closing in fast.
"Something's coming! Get ready!" the captain shouted.
But before he could finish, the stone pavement exploded. A massive, purple-black shadow burst from the ground, coiling like a giant snake. It seized the captain, hoisting him into the air. In an instant, it pierced his chest, tearing through his organs. Blood and flesh sprayed like rain, filling the air with a sickening stench.
"What is that?!" a soldier cried.
Boom! Boom!
The ground kept erupting as countless purple-black tentacles surged upward, each as thick as a tree trunk. They smashed through houses like paper and swept through the cavalry, snapping bodies in half, devouring organs, and flinging remains aside.
In mere minutes, nearly a hundred armed soldiers were slaughtered.
The tentacles slowly retracted, pressing against the ground to lift a massive section of the street, revealing a colossal figure wreathed in purple-black flames. Two glowing red orbs, like giant lanterns, marked its head—its eyes.
"Lord Moryo!" a group of ninja emerged from hiding, gazing at the creature with fanatical awe.
The monster's gaze shifted to another side, where two figures in black robes with red clouds stood.
"Lord Moryo," one of them said, bowing slightly. "As agreed, we've broken your seal and helped you consume every living soul in Ogutani Castle. Now, it's your turn to uphold your end of the bargain, isn't it?"