Inside the Kitahara residence, beneath the bright lights of his room, Kaede Kitahara set down his diary. At the same time, a translucent panel flickered into existence before him.
It was time for the draw again.
"Stop!"
At his command, the spinning pointer halted, finally landing on an option that made his eyes widen.
"Thunder Breathing: From Beginner to Mastery."
Kaede froze for a moment. Thunder Breathing… wasn't that one of the breathing styles from Demon Slayer?
How was he pulling skills from an entirely different world inside Naruto?
He quickly selected "accept," and in an instant, a flood of information surged into his mind. As expected, it was exactly the Thunder Breathing from Demon Slayer.
This time, he had obtained the complete set—every sword form of Thunder Breathing, including Thunderclap and Flash, Rice Spirit, Thunder Swarm, Distant Thunder, Heat Lightning, Rumble Thunder, and Flaming Thunder God.
Alongside that came the layered training methods for each stage of the breathing technique.
The first stage was Total Concentration Breathing. Once achieved, it allowed the user to temporarily enhance their physical strength and gain the ability to kill demons. Most members of the Demon Slayer Corps remained at this level, which was sufficient for dealing with ordinary demons.
The second stage was Total Concentration: Constant. Reaching this level required maintaining Total Concentration Breathing twenty-four hours a day, even while eating and sleeping. Once mastered, it brought a tremendous boost to physical conditioning.
The third stage involved awakening the mark. At that level, a swordsman's strength would become even more astonishing.
And the final stage was the Transparent World. Upon reaching it, the user could conceal their presence while sharpening their perception through precise control of breathing and movement. They would be able to clearly observe an opponent's breathing patterns and blood flow, greatly improving their ability to predict movements and dodge attacks. The effect was almost like activating both the Sharingan and the Byakugan.
However, this version of Thunder Breathing had been modified for the ninja world.
In the original Demon Slayer world, the overall power level was relatively low. Aside from Muzan's immortality and Blood Demon Arts, most abilities didn't reach particularly high levels.
Those flashy visual effects produced by the breathing styles—water, lightning, flames—weren't actually real. Even the original author had explained that they were more like visual impressions. The sword strikes of ordinary corps members were the true baseline, while the elemental effects were essentially illusions created through impact.
It was all a trick of perception.
At its core, it was just overwhelming force.
Especially the Stone Hashira—could that even be called a breathing style? The man swung a massive hammer like he was piloting a helicopter, and still claimed it was part of his breathing technique.
But this modified version was different. Instead of relying purely on breathing to push the body's limits, it worked in conjunction with Lightning Release chakra.
The result was that its power far surpassed what it could achieve in the Demon Slayer world.
And even if one awakened the mark, it wouldn't come with the original drawback of dying before the age of twenty-five. In Demon Slayer, there had been no supernatural energy system to compensate, so the body had to be pushed to its absolute limit at a terrible cost.
Here, chakra provided that compensation, eliminating the need for such a price.
"Let's test it out."
Kaede pulled out the Sword of the Thunder God. The weapon itself carried lightning properties, making it perfectly suited for Thunder Breathing.
With a blur, he vanished from the room. When he reappeared, he was already deep within a forest on the outskirts of Konoha.
The night echoed with the roars of wild beasts. This was part of the Forest of Death, a place rarely visited, often used by shinobi for training.
"Let's start."
Kaede smiled faintly and channeled chakra into the Sword of the Thunder God. Instantly, a vast surge of energy roared to life, far exceeding what it had displayed in Rokusho Aoi's hands.
The sheer pressure of the blade sent nearby beasts scattering in panic.
Even without intelligence, they could sense its danger.
"Thunder Breathing, First Form: Thunderclap and Flash."
In an instant, Kaede's body was wrapped in brilliant lightning. He shot forward like a bolt of thunder.
A deafening roar tore through the forest.
Everything in his path was shredded apart, trees collapsing as he cut through them. Only after slicing cleanly through a massive trunk did he finally come to a stop.
"While using the sword forms, it's similar to a Lightning Release chakra mode. The speed boost is incredible."
He quickly assessed the results.
Speed was the defining trait of Thunder Breathing. Once activated, it drastically amplified the user's movement speed, and Kaede's own had nearly doubled.
The First Form provided the greatest speed increase, and its destructive power was equally impressive. A single swing of his blade rivaled an A-rank jutsu.
The enhancement it provided was already comparable to the first four gates of the Eight Gates. Of course, the later gates were on an entirely different level—opening the eighth could even severely injure Six Paths-level opponents.
That was a different matter altogether.
As he came to a halt, the lightning around him faded instantly.
At present, Kaede could only maintain Total Concentration Breathing while actively focusing, which meant he still needed to dedicate full attention during execution.
That placed him at the level of an ordinary Demon Slayer Corps member.
Next, he needed to reach Total Concentration: Constant—the point where the breathing technique could be maintained twenty-four hours a day, even during sleep.
It felt somewhat similar to keeping the First Gate open at all times.
Now that he could already maintain the First Gate as a baseline state, unlocking the brain's limitations and gaining full control over his body, it explained why he had been able to use Thunder Breathing almost instantly.
His body could fully obey his will. As long as he didn't exceed his limits too drastically, he could push it to perform.
That was the terrifying aspect of maintaining the First Gate.
With Thunder Breathing added to his arsenal, Kaede's strength rose another step. He was no longer just at the entry level of Kage-tier. His physical power had grown even further.
Combined with the Uzumaki Clan's Sage Body, the full potential of Thunder Breathing could finally be realized.
The next day, Kaede rested at home. After training through the night, he had already begun to grasp the threshold of Total Concentration: Constant. Thanks to his experience maintaining the First Gate, progressing to the second stage of the breathing technique was far easier.
He didn't summon the members of Team 7 or his own squad today. There were no missions for the next couple of days, and the Ninja Clash in the Land of Snow assignment Kakashi had entrusted to him wouldn't begin for another two days.
For once, he had some rare downtime.
What he didn't expect was Uchiha Sasuke showing up early in the morning, dark circles under his eyes.
What was he doing all night…?
Kaede found it a little strange, but still gestured for him to sit.
He had no idea that the diary update from the night before had kept Sasuke awake the entire time, his mind racing.
He had been thinking about his relationship with Itachi. About how to kill Uchiha Kenji. About how to kill Shimura Danzo. And most of all, whether he should abandon Konoha.
According to the original timeline, he would eventually defect and follow Orochimaru.
But later, he would realize Orochimaru wasn't someone to trust, and in the end, he would return to Konoha, even settling down and starting a family.
If that was the case, then why leave in the first place?
It would only complicate things further… even affecting his future child.
From Kaede's diary, Sasuke had learned why his future self chose to leave Konoha and follow Orochimaru. But the reason he eventually chose to return—and build a life there—had not been revealed.
So he didn't dare act recklessly.
He believed that his future self must have had a reason for making those choices.
Still, he needed strength.
He couldn't follow Orochimaru, but that didn't mean Konoha lacked powerful shinobi. Publicly, the Third Hokage still stood at the top, though Sasuke had no expectations of him. His own teacher, Hatake Kakashi, was clearly on the verge of stepping into Kage-level strength.
Despite Kaede's teasing about him always ending in a draw, Sasuke had seen Kakashi's strength firsthand. Even now, with Kakashi only just resuming his training, Sasuke still found himself completely overwhelmed.
If Kakashi got even slightly serious, it was enough to make Sasuke understand what it meant to be crushed by reality.
And beyond those two, there was an even better option.
Kaede Kitahara.
On the surface, Kaede was just an ordinary chunin, not even a jonin yet, having only recently reached that rank.
But from the diary, Sasuke knew the truth—Kaede already possessed genuine Kage-level combat power, or at the very least, strength capable of matching it.
To Sasuke, that was an entirely new path.
There were other reasons as well. Compared to Kakashi, Sasuke felt more inclined to draw closer to someone who, despite not sharing his surname, was still part of the same clan.
That was why, despite his pride, he hadn't argued back when Kaede lectured him before.
It also explained why Kaede found Sasuke's attitude unusually agreeable, nothing like the stubborn, prideful "Sunny Sasuke" he knew.
After all, Kaede was one of the few remaining members of their clan.
But more than anything, Sasuke wanted to know one thing.
How Kaede had reached Kage-level strength… without a Mangekyō Sharingan.