At Aokiji's suggestion, Yorichi Tsugikuni really did switch to a bamboo sword. True to his word, Aokiji immediately used his Devil Fruit powers to craft a sword of ice.
Though calling it an ice "sword" wasn't quite accurate. The weapon Aokiji created was shaped like a sword, but it didn't have a sharpened edge at all. Its blade was essentially a solid rod, perfect for sparring without risking injury to Yorichi.
A moment later, the two of them clashed fiercely on the deck.
Without his Devil Fruit powers, Aokiji's physical skills were clearly lacking. Even when fighting a "rookie" like Yorichi, he only barely managed to maintain a slight advantage.
During the spar, Aokiji demonstrated the other techniques of the Navy's Rokushiki.
There was Kami-e, or "Paper Art," which involved sensing the flow of air during an opponent's attack to predict the direction and use muscle control to dodge fluidly.
There was Geppo, or "Moonwalk," an advanced evolution of Soru that allowed the user to remain briefly airborne by kicking the air at high speed.
There was Rankyaku, "Tempest Kick," in which a rapid kick sliced through the air to unleash an invisible blade of compressed wind.
There was Shigan, "Finger Pistol," a technique that focused the entire body's force into a finger thrust, powerful enough to pierce human flesh like a bullet.
And finally, there was Tekkai, "Iron Body," which accelerated blood flow and channeled power into a finely trained physique, making the body as hard as steel and able to shrug off bullets or sword slashes.
These five abilities, combined with the high-speed movement of Soru, formed the complete set of the Navy's Rokushiki.
As they sparred, Aokiji demonstrated each technique in turn. And Yorichi, with his Transparent World, could easily see through the essence and mechanics of every move.
At its core, all of these techniques were simply forms of extreme bodily control. And Yorichi's greatest strength wasn't merely the terrifying power that let him unleash a hundred sword strikes in an instant. It was his unrivaled control over his own body.
In the world of Demon Slayer, anyone who had mastered the Breathing Techniques to their utmost and reached the domain of the Transparent World possessed astonishing control over their muscles and physical functions.
This incredible mastery, combined with Yorichi's natural physical prowess, allowed him to flawlessly replicate each Rokushiki technique the moment he understood its inner workings.
As Yorichi grew more adept at performing the Navy's Rokushiki, he began contemplating how best to integrate these techniques into his own fighting style.
"The way Shigan generates force is quite similar to the seventh form of Sun Breathing: Yang Bright Thrust."
"Except one channels power into the fingertip, while the other channels it into the sword tip."
"For me, Shigan isn't all that useful."
"Geppo could help me gain brief airtime, but with swordsmanship, true power comes from having solid footing. In a normal fight, it would only be useful for catching the opponent off guard."
"Soru, though… that's pretty handy. It would let me chain sword techniques together much more smoothly."
"Rankyaku seems extremely practical. If I could perform it using my sword, wouldn't that essentially become a flying slash attack?"
"As for Tekkai… yeah! That's the one I need most right now. Everyone knows swordsmen are notoriously fragile when it comes to defense!"
"Tap!"
"Tap!"
"Tap!"
On the deck, Yorichi's bamboo sword and Aokiji's ice "rod" clashed again and again, producing a series of deep, heavy thuds. Yorichi's attacks flowed like water, and even without employing any formal sword techniques, his strikes connected one after another with seamless precision.
Although each individual blow wasn't especially powerful, every strike was directed toward openings in Aokiji's defenses.
Aokiji, meanwhile, found himself reduced to constant defense, gripping his ice rod and relying on his speed and occasional subtle uses of Observation Haki to block Yorichi's relentless strikes.
But each time Aokiji tried to switch from defense to offense, Yorichi would shift tactics at just the right moment, forcing Aokiji to abandon any thought of attacking and return to defending instead.
More than once, Aokiji wondered if this kid Yorichi might actually know Observation Haki as well, combining it with his excellent swordsmanship to keep Aokiji pinned down.
But then Aokiji shook his head self-deprecatingly. He'd never taught Yorichi Observation Haki, and he knew that a kid who'd only just learned the Rokushiki couldn't possibly have mastered such an advanced ability already.
What Aokiji didn't know was that while Yorichi indeed hadn't learned Observation Haki, he possessed the Transparent World.
The subtle shifts in Aokiji's muscles whenever he attempted to switch from defense to offense were plain as day to Yorichi's eyes. If Observation Haki functioned by "sensing" an opponent's intentions, then Yorichi's Transparent World achieved the same result by "seeing" the physical changes in an opponent's body.
The difference was akin to the contrast in the world of Naruto between the Uzumaki Clan's Kagura Mind's Eye and the Hyuga Clan's Byakugan.
Eventually, the commotion from Yorichi and Aokiji's spar drew the attention of sailors all over the ship.
Now that the ship's course was firmly set, most of the Marines not stationed in the engine room, helm, or lookout tower didn't have much to do. Many who'd been strolling around the deck idly began noticing the battle taking place.
Word spread quickly, and before long, a crowd of sailors had gathered around the deck, pointing and murmuring as they watched Aokiji and Yorichi duel.
"Hey! That red-haired kid looks familiar. Isn't he the one from Ryugin Island?"
"Yeah, the one Vice Admiral Garp brought aboard. I remember now Yorichi Tsugikuni! Wasn't he stationed at Headquarters? How's he on the ship now?"
"You didn't hear? Vice Admiral Garp brought him along when they set sail. I heard he's a disciple of Admiral Zephyr now."
"Wow! A student of Zephyr-sensei? But isn't this kid a little too strong? Back in the East Blue, he didn't seem anywhere near this powerful. Now he's going toe-to-toe with Captain Kuzan?"
The Marines' chatter reached the ears of both Yorichi and Aokiji. Yet neither of them paid any attention, staying fully focused on their duel.
Quite a few of Garp's crew recognized Yorichi, since he'd originally traveled aboard this very ship to join the Navy.
Some of the sailors had even fought alongside him before.
Those who'd seen him previously were astonished to find that Yorichi's strength had grown significantly since his days in the East Blue. His use of Soru had become exceptionally refined, allowing him to vanish and reappear in sync with his dazzling swordsmanship. His combat power seemed to have multiplied exponentially.
Yorichi himself was keenly aware that while his Doriki value might not have increased, his practical combat ability had improved dramatically. The current him could probably defeat his former self in fewer than five moves.
People always claimed Kaido was the greatest teacher in the One Piece world, but if you asked Yorichi, Aokiji wasn't too shabby either.
"Hyaaah!"
On the deck, Aokiji finally managed to find a gap in Yorichi's offense. With a swift movement, he used his ice rod to parry Yorichi's bamboo sword and countered with a thrust aimed straight at Yorichi's abdomen.
After all, Yorichi was still just twelve. He didn't have the stamina reserves of an adult like Aokiji.
The prolonged fight had begun to wear him out. Maintaining "Total Concentration Constant" breathing and repeatedly using Soru had drained Yorichi's strength rapidly.
By now, exhaustion was slowing his movements, and Aokiji seized the opportunity to strike back.
"Tekkai!"
Seeing Aokiji's ice rod speeding toward him and knowing he couldn't dodge in time, Yorichi instinctively called out in his mind, planning to use Tekkai to endure the hit. But the instant the rod connected, he felt a tremendous impact slam into his abdomen, sending him flying through the air.
"Thud!"
Yorichi's body hurtled backward, sailing more than ten meters before crashing into the ship's mast and finally coming to a stop. As he collapsed to the deck, his head spun dizzily, nausea surging through him until he couldn't help retching up a mouthful of clear liquid a fresh victim of Tekkai's brutal side effects.
"Hey, are you okay?" Aokiji quickly ran over, genuine concern in his voice. After being on the defensive for so long, he hadn't held back once he found his opening. Now, seeing Yorichi in such rough shape, he felt a pang of guilt.
"Bleh… I'm not hurt!"
"Tekkai is amazing!"
After quite some time, Yorichi finally regained his senses and staggered to his feet. As he tested his body, he was astonished to discover that he wasn't injured at all. In the past, a hit like that would have completely taken him out of the fight.
"Heh."
"Bogart, starting tomorrow, you'll teach him Haki."
"There's no need for him to keep training in Rokushiki. He's already mastered it."
Up in the lookout tower, Garp watched as Yorichi bounced back to his feet. Letting out a quiet chuckle, he spoke to his adjutant, then turned and left the tower.