Early next morning, at the Fifth Division barracks.
Aizen watched Naraku Sora from a short distance away, his gaze almost entirely fixed on the boy's hands.
Basic Kidō circuits, surging, dense Reiatsu, and that sharp "edge" that only belonged to swordsmanship.
Every time he thought he'd finally seen the limit of Naraku's potential, this guy managed to jump out and blindside him with something insane.
"If you were just coating your Zanpakutō in Kidō and using it as a medium to fire the spell, that'd only count as inventing a new Kidō," Aizen said casually.
Even though he'd only just graduated from the Academy, there weren't many people with a deeper understanding of Kidō than him.
And that was with him intentionally holding back.
"You can take Hadō #78, Zangerin, as a reference. Its outward form is almost identical to a sword technique."
He paused for a moment, then his lips curved faintly.
"Like other Kidō, every part of Zangerin—from the prep motion to the actual swing—is part of the spell's structure. You can think of it as a physical version of the chant."
"Likewise, experts can release Zangerin using different movements—that would count as another kind of chantless casting."
Naraku nodded in dawning understanding.
Information on that spell surfaced automatically in his mind.
If he remembered right, he had a "discount senior" who was pretty good at it—too bad it had never done anything particularly useful in a real fight.
"You're different, though, Sora."
Aizen hesitated at the way he addressed him; it felt a bit too familiar. But for the sake of the persona he was playing, he didn't have much choice.
"What you've created—let's call it Kidō-swordsmanship for now—"
"Almost perfectly fuses Kidō and swordsmanship, breaking the boundary between them. It gives your attack the properties of both at once."
"Just pulling off a move like this is enough to etch your name into Soul Society's history."
Naraku grinned. "You flatter me. Just dumb luck."
Aizen pressed his lips together, his gaze turning complicated.
He'd assumed Naraku came today to ask for help with training.
He hadn't expected the kid to dump a world-shaking technique on him instead.
He'd thought that over time, the difference in strength between them would only grow, stretching farther and farther out of reach.
Yet not long after graduating, that gap had suddenly shrunk by a huge margin.
Sometimes Aizen wondered if he'd spent a little too much time buried in paperwork, neglected his own training, and given Naraku room to catch up.
But thinking about it calmly—no normal Shinigami progressed like this.
Reiatsu at Grade 10, yet punching up and forcing Grade 6 Shinigami into a corner?
Wait—
Aizen's pupils narrowed, a flash of shock flickering in his eyes.
Naraku's Reiatsu…
Grade 7?
Even though Naraku hadn't fully released himself, Aizen could still sense something from the Reiatsu that leaked out when he used that original technique.
He prided himself on having decent talent for Reiatsu—but not this kind of growth.
In just a few days, from Grade 10 to Grade 7.
At this rate, the brat really would take the Captain-Commander's seat one day.
How long had it taken him to climb from Grade 10 to Grade 7?
A month? Two?
In all Soul Society's history, he'd never found another Shinigami more gifted than himself.
But compared to the guy in front of him, maybe he was just… average.
While Aizen was spiraling, Naraku grinned and suddenly said:
"Right, Aizen—why don't I teach this to you? You can help me refine it."
Aizen: "?"
"Did you hit your head this morning?"
"Lieutenant Aizen, I'm perfectly clear."
"If you were, you wouldn't spout nonsense like that," Aizen replied, a hint of exasperation crossing his face. "I'm not exaggerating when I say merging swordsmanship and Kidō is a groundbreaking achievement."
"Starting a whole new school of combat wouldn't be an overstatement."
"For example—Head-Captain Yamamoto's position isn't just because his raw strength is overwhelming. His founding of the Genryū style is inseparable from it."
"Or more precisely, the two are intertwined. Genryū was Yamamoto's foundation in his early years."
"Because Genryū existed, people gathered around him. That's how the original Gotei 13 was born."
"And now you're saying you want to hand your life's work to someone else."
Naraku just laughed. "Think of it as an advance investment. When you're a big shot later, don't forget to pull your dear brother up."
"Besides, I am asking you to help me refine it."
Aizen blinked, clearly not having expected that answer.
"All right, stop spacing out."
"Let's start from the basics of swordsmanship."
...
...
Because Naraku wasn't great with technical terms, his teaching usually went something like "do this, then do that" instead.
If that didn't work, he'd just show it himself.
Obviously, this teaching style would be borderline useless for any normal Shinigami.
But since Aizen knew him well, he could quickly parse what Naraku meant, digest it, and turn it into something usable.
Even so, the whole process reminded Naraku a bit too much of Naruto teaching Konohamaru the Rasengan.
Come to think of it, Konohamaru being able to learn the Rasengan from Naruto probably did mean he was a genius.
Just as the two of them were discussing whether higher-tier Kidō could be woven into the technique, a Shinigami burst into the dōjō.
"Ninth Seat Aizen, urgent deployment order!"
The messenger was breathing hard, face anxious, as he held the mission slip up high.
"The Shinigami assigned to West Rukongai's District 3, Koi-Fushi Mountain, has gone missing. He failed to report back during today's debrief."
Aizen frowned and instinctively glanced at Naraku.
"I understand."
"The mission is urgent. Please depart immediately," the messenger reminded him, then hurried off—probably to pass orders to others.
"Take me with you!"
Aizen had just opened his mouth when Naraku cut him off.
"I can't stand people who break the law and do whatever they want."
Naraku's eyes were shining, his whole body itching for action.
Aizen gathered up the scattered bamboo swords in the dōjō, face unreadable.
"A Shinigami going missing in their assigned sector isn't common. When it happens, it's often something very serious."
"There's a good chance this mission will go sideways."
"So…"
He looked up, voice calm.
"Be careful."