The Most Terrifying Swordmanship  

Seeing Rukia reach her limit, Ailin quickly called a halt to their spar.

Clang!

As soon as Ailin spoke, Rukia's grip loosened, and her Asauchi clattered to the ground.

"Haah... haah..."

Rukia leaned forward, hands on her knees, gasping for breath. The fear in her eyes hadn't faded. If she had a choice, she never wanted to fight Teacher Ailin again. The feeling of being completely seen through, every move anticipated, was utterly terrifying.

"Rukia, what are your thoughts on that spar?"

"Thoughts?" Rukia managed a weak smile. "Teacher, my biggest thought is that I never want to fight you again."

"Is that so?" Ailin wasn't surprised by her response. It was exactly what he had expected.

The "Data Kendo" he planned to teach Rukia originated from a tennis game he had played with Haruko.

There was a time when Haruko had utterly dominated Ailin in the game of chess. Determined to find some balance, he had introduced the sport of "tennis" to the Soul Society centuries ahead of its time.

He had also created replicas of the rackets used by the "Princes of Tennis" from a manga he remembered. To his surprise, when he transformed these rackets into Zanpakutō, the abilities of the most skilled players proved to be no weaker than those of captain-level Shinigami.

The "Data Kendo" he was about to teach Rukia was derived from the "Data Tennis" wielded by one of these tennis prodigies.

Anyone who had faced an opponent using "Data Tennis" would find it difficult to muster the will to fight them again.

In the eyes of a "Data Tennis" player, your every move provided valuable information, allowing them to construct a model of your play style and analyze your thought process.

If a "Data Tennis" player fully deciphered your game, and they possessed sufficient skill, the match would become completely one-sided. They would win a hundred, a thousand times in a row.

To them, anyone they had completely analyzed was nothing more than a puppet, their every move predictable. You were like a fly caught in a spider's web, destined to be consumed once you exhausted yourself struggling.

In Ailin's view, "Data Kendo" was perhaps the most terrifying form of swordsmanship imaginable.

After adapting "Data Tennis" into "Data Kendo," he realized that Rukia was the perfect candidate to learn this technique.

Firstly, Rukia's analytical mind was ideally suited to "Data Kendo."

Secondly, Rukia's Zanpakutō, Sode no Shirayuki, was the most beautiful Zanpakutō in the Soul Society. Its ability was to freeze anything it touched by lowering the user's body temperature to below freezing. However, before Rukia could fully master this power, Sode no Shirayuki had extended its ability to the blade itself, allowing Rukia to use it without freezing her own body.

This compromise meant that Sode no Shirayuki's freezing power couldn't be fully realized. After all, it was one of the "strongest" Zanpakutō, on par with Ryūjin Jakka, Hyōrinmaru, and Sōō Zabimaru.

Unlike Hyōrinmaru, which condensed moisture from the air to create ice, Sode no Shirayuki itself was the embodiment of "coldness," capable of freezing anything it touched. Theoretically, it wouldn't be countered by Ryūjin Jakka.

If Rukia's reiatsu reached the level of Captain-Commander Yamamoto, she would pose a genuine threat to him.

Of course, the stronger Sode no Shirayuki's ability, the more demanding its requirements. If the user was careless, they could be severely injured by their own Zanpakutō. But if Rukia learned "Data Kendo," these drawbacks would no longer hinder her. In fact, it would allow her to master Sode no Shirayuki's power even faster.

"Rukia, although I didn't draw my sword during our spar, I was using my 'Data Kendo' from the very beginning. To my 'Data Kendo,' you hold no secrets. And this is what I intend to teach you."

"What? This is 'Data Kendo'?" Rukia looked up in astonishment. The fear she had felt transformed into excitement. Only after experiencing that despair firsthand could she truly grasp the terrifying nature of "Data Kendo."

"Indeed. However, Rukia, mastering true 'Data Kendo' is no easy feat. If you fail to learn it properly, your swordsmanship may stagnate, or even worse, you could lose your ability to fight in close combat, becoming a Shinigami who relies solely on Kidō."

"So, Rukia, are you sure you want to learn this Swordsmanship, even with its potentially severe consequences?"

Ailin wasn't exaggerating. If someone attempted to learn "Data Kendo" but lacked the ability to rapidly gather information, they would be easily defeated by their opponents, their attention divided between fighting and collecting data.

If they couldn't overcome this "mental habit," they would be forever barred from close combat.

Of course, even then, applying "Data Kendo" to Kidō would still significantly enhance Rukia's strength.

"Yes, Teacher, I want to learn it! Please teach me." Rukia retrieved her Asauchi and bowed deeply to Ailin.

"Hahaha, I was always going to teach you this. If you're willing to learn, I'm willing to teach."

Ailin and Rukia returned to the cherry blossom tree and sat down. Then, Ailin began describing the training method for "Data Kendo."

"Rukia, 'Data Kendo' is entirely based on 'data.' 'Data' is simply a way of quantifying everything in the world using a system we can understand. For example, if you swing your sword and leave a one-millimeter mark on a Sekkiseki stone, we'll assign a value of '1' to the power of your strike."

"In battle, if your movement and evasion speed is ten meters per instant, we'll quantify that speed as '1' as well."

"For defense, we'll quantify the amount of force required to injure you as your defense, also using '1' to represent it."

"This way, we can quickly obtain your accurate data."

"The essence of 'Data Kendo' is to 'know yourself and your enemy, and you will never be defeated.'"

"Once you understand your own data, the next step is to gather data on your opponent."

Under the cherry blossom tree, Ailin continued his explanation, and Rukia listened intently. When she encountered something she didn't understand, Ailin paused, using examples from the Soul Society to aid her comprehension.

Ailin was completely engrossed in his teaching, oblivious to the passage of time. Rukia, eager to improve her strength, also paid no heed to the changing sky.

Haruko had come by once, but seeing Ailin so absorbed in his lesson, she didn't interrupt. Instead, she went back to arrange accommodations for Toshiro Hitsugaya.

"Oh my..." Ailin stretched, realizing that he had been teaching for far longer than intended.

He didn't mind, but Rukia had reached her limit. Continuing would only waste time.

"Rukia, it's been ages since I've taught a student so thoroughly. I got carried away, and now it's almost dawn."

"Your first task, Rukia, is to successfully quantify all of your own data. Once you've accomplished that, I'll teach you the next step of 'Data Kendo.'"

"Yes, Teacher." Although she was eager to learn more about "Data Kendo," Rukia knew she had reached her limit after over ten hours of intense study. Once she fully grasped everything Ailin had taught her today, she would be ready to embark on the path of "Data Kendo" after completing her "datafication."

…

With Ailin disguised as 5th Division Captain Sōsuke Aizen refraining from causing trouble, the Seireitei remained peaceful.

Occasionally, Ailin would spare some time to guide the Shinigami who had aligned themselves with Aizen, ensuring their steady progress.

In recent years, he had focused his attention on Hueco Mundo. After all, using the Hōgyoku to enhance his reiatsu was more convenient there.

In Hueco Mundo, Nnoitra Gilga and Szayelaporro Granz didn't dare to take Ailin's words lightly. They scoured Hueco Mundo in search of a suitable replacement for Nelliel Tu Odelschwanck.

Nnoitra had actually found a potential candidate - a female Vasto Lorde whose strength even he had been unable to match before she became an Arrancar. However, instead of killing or devouring Nnoitra, this female Vasto Lorde had spared his life.