Intervening Existence  

Kugo Ginjo, aware his attack hadn't fazed Ailin, had used the chaos of the Cero and Yukio's game space to escape with his companions. Ailin wasn't surprised. However, as he surveyed the scene, his gaze fell upon a lifeless body lying near the remnants of the mansion, and a sardonic smile tugged at his lips.

It was almost laughable. In the midst of a seemingly ordinary battle, Ginjo had neglected to protect his own physical form. While the brunt of the Cero had been directed at Ailin, the mere shockwave of the attack was enough to prove fatal for an ordinary human.

Yukio and the others, in their haste, had only managed to extract Ginjo's soul, leaving his body behind. In its current state, even if Ginjo's soul returned, he wouldn't last three minutes.

Humans possessed a unique advantage - their capacity for growth. Now, without a body, Ginjo's potential had drastically diminished. Even with the addition of more Fullbring powers and Hollowfication, Ailin estimated Ginjo's strength would be capped at the peak of captain-level.

Unless, of course, Ginjo chose to hoard Ichigo Kurosaki's Fullbring power for himself a century later, refusing to share it with the other members of Xcution. Otherwise, reaching the level of a "hundred-year captain" would remain a distant dream for Ginjo.

Ailin collected Ginjo's body. Though he hadn't managed to eliminate Ginjo's soul, acquiring his corpse was sufficient to appease Jushiro Ukitake. With Ginjo's trail lost, Ailin abandoned the pursuit.

This encounter would surely leave Ginjo with a lingering fear of Ailin for decades to come, forcing him to operate in the shadows. Moreover, until he figured out a way to circumvent the monitoring function of the Substitute Shinigami Badge, Ginjo wouldn't dare utilize it, likely entrusting it to Yukio for safekeeping within his game space, away from the watchful eyes of Soul Society.

Ailin ascended into the air with his palm facing the burning remains of the mansion. "Hadō #58: Tenran!" A swirling tornado erupted from his hand, rapidly expanding and extinguishing the flames. The once opulent mansion was now reduced to smoldering debris.

Instead of immediately returning to Soul Society, Ailin settled down amidst the ruins, assuming a meditative posture. During the fight with Ginjo, Tsukishima's blade had pierced Ailin's foot. Now, Tsukishima's "existence" was beginning to infiltrate Ailin's memories.

Ignoring the influx of foreign memories, Ailin entered his own inner world, Unlimited Blade Works, through "Jinzen." With a gesture, a long sword rose from the countless blades at the base of the hill, flying into his hand.

"Book of the End..." Ailin murmured, recognizing the sword's name and abilities. It could transform a person's life into a book, allowing the user to insert their own "existence" into any point in that person's past, forging a connection with them.

Understanding its power, Ailin released the sword, and it returned to its place among the captain-level Zanpakuto on the hill.

Exiting Unlimited Blade Works, Ailin drew his own Zanpakuto, transforming it into a katana with a single thought. He then swung the blade towards his own hand.

"Shhh!" The katana passed through his arm as if it were a mere illusion. However, Ailin sensed an anomaly within his arm – a foreign reishi carrying his memories, yet under his control. This foreign reishi was attempting to rewrite information within his soul.

With a flick of his mind, Ailin assimilated the foreign reishi.

The world spun...

...

Ailin, a ten-year-old boy, found himself amidst the familiar setting of the Shin'ō Academy, specifically Class 1-C. From today onwards, he would study here, aspiring to become a powerful Shinigami.

He wondered when his "cheat" ability, common among transmigrators, would manifest. Would it activate upon absorbing his first strand of reishi or refining his first wisp of reiryoku? Or perhaps he needed to acquire his Zanpakuto first?

As long as it wasn't the kind of "cheat" that only appeared after he became a captain, Ailin would be content.

Scanning his classmates, he didn't recognize any familiar faces. It made sense; his transmigration had occurred over two hundred years before the main storyline. Most of the individuals he knew were either already serving in the Gotei 13 or hadn't been born yet.

However, his gaze caught sight of a boy with black, medium-length curly hair sitting in the front row. His pupils constricted.

That person – despite appearing much younger than in his memories, having transformed from an adult into a teenager – his features, the book in his hand, all pointed to one name –

Shūkurō Tsukishima!

"Impossible! How could Tsukishima be here in Soul Society at this time, and in the same class as me?" Ailin covered his face, concealing his shock as he tried to regain his composure.

"Something's wrong, very wrong," he thought. "If my memories are accurate, Tsukishima was adopted by the first Substitute Shinigami, Kugo Ginjo, and later formed the Xcution organization with him...

But at this point in time, Ginjo might not even be born yet. How could Tsukishima be here in Soul Society?"

A thought struck him as he recalled Tsukishima's abilities.

"That's right, Tsukishima's ability allows him to insert his existence into the past of his enemies, changing their perception of him and making them view him as a 'friend' worth dying for.

Could it be that the future me is currently battling Tsukishima and has already been struck by his blade?"

Ailin, his face still hidden, felt a mix of emotions. Relief that he would become a Shinigami and survive until the end of the Aizen arc. But also a sense of dismay – his strength, it seemed, wasn't as exceptional as he had hoped.

He remembered that Tsukishima's power in the future was roughly equivalent to that of a captain-level Shinigami. To be able to fight Tsukishima, Ailin himself must also be a captain of one of the Gotei 13 divisions.

However, being struck by Tsukishima's blade and having his existence interfered with meant that his strength was likely on par with Tsukishima's.

Perhaps in times of peace, such strength would be sufficient. But just a few years after the Aizen arc came the "Thousand-Year Blood War."

Could he survive the onslaught of those Quincy?

That day, Ailin remained in a daze, barely registering the words of his teacher.

That night, lying in his dorm, Ailin contemplated his uncertain future. Suddenly, he sat up in bed, a glimmer of hope emerging.

"No, wait, I still have a chance to change my fate!"

He recalled that after Tsukishima intervened in someone's existence, he would also undergo training alongside them, learning their weaknesses and carrying the strength gained during that period back to his own time.

So, if Ailin started training diligently from this point onwards, pushing himself to the limit, would his strength also increase by the time his memories returned to the battle with Tsukishima?

Taking a deep breath, Ailin decided to give it a try. After all, things couldn't get any worse than they already were, could they?

"Although I don't know my current strength, I do know that in a Shinigami's battle, besides various powerful abilities, swordsmanship is paramount.

Since I managed to become a captain before Tsukishima's intervention, I must have some proficiency in Shunpo, Hakuda, Kidō, and Zanjutsu.

Tsukishima's intervention simply adds the time he spent with me to my memories. So, even without interacting with him, I'll ensure he remains within my sight. And then, I'll dedicate all my time to training in swordsmanship!"

With a plan in place, Ailin's days at the Shin'ō Academy took a drastic turn. He abandoned all other subjects, focusing solely on swordsmanship. He believed that as a captain, he might lack a powerful, one-hit kill technique. Therefore, he resolved to develop his ultimate move within the next hundred years.

Initially, Ailin thought he would need to seek out Tsukishima deliberately. However, he soon discovered that as long as he began his training, Tsukishima would appear within his peripheral vision.

This realization brought Ailin immense relief.

"Future me, when you recall this memory, please don't forget my efforts..."

Four years passed in the blink of an eye. Ailin transitioned from a first-year student to a fourth-year student. His peculiar behavior – neglecting Kidō, Hakuda, and Shunpo, focusing solely on swordsmanship – had turned him into an oddity within the academy.

At first, Ailin had trained in basic swordsmanship alongside his teacher. But gradually, he abandoned everything else, focusing on a single strike – the cut. With each swing of his blade, he poured all his strength, even exceeding his limits, into that one strike.

This resulted in Ailin consistently achieving the lowest scores in the annual promotion exams. In the other three subjects, his grades were zero. Only in swordsmanship did he manage to achieve some level of proficiency. Within Class 4-C, there were no more than three students who could withstand a single strike from Ailin.

Aware of Tsukishima's motives, Ailin refrained from interacting with him throughout these four years. However, there were several instances where Tsukishima, observing Ailin's training, offered corrections to his posture. Ailin would experiment with the suggestions, adopting them if they proved helpful, and continuing his training.

He was essentially taking advantage of Tsukishima's presence.

One day, as Ailin practiced his Iaido, a sudden shiver ran down his spine, and his gaze sharpened.

"This is... the time when I was still studying at the Shin'ō Academy?"

"I succeeded!"

A smile crept onto his face, but he quickly composed himself, closing his eyes to examine his memories.

Due to his actions being slightly slower than Tsukishima's, Ailin's memories revealed that Tsukishima had appeared during his first year at the academy. And although Ailin was only about fifteen minutes behind Tsukishima in real time, Tsukishima's reishi had already infiltrated his memories up to his fourth year at the Shin'ō Academy.

However, as Ailin absorbed the memories of his "past self," he couldn't help but feel a sense of amusement.

"Just how much did my past self distrust my future self?" he thought. "To think that Tsukishima's ability could pose a threat to me..."

"And to prepare a killing blow for myself, I even trained this 'swordsmanship' technique as my ultimate move right before Tsukishima's eyes?"

Touching the sword at his waist, a smile returned to Ailin's lips.

"Well, since this was my wish, I'll fulfill it for my 'past self'. For the next hundred years, I'll focus on perfecting this one strike!"

With Ailin's current level of swordsmanship, the single strike he had practiced for four years was nothing extraordinary. However, it was a precious gift from his "past self" to his "present self"...

"Rest assured," Ailin thought, "I'll refine this strike to its utmost potential, making it one of my strongest killing blows in the future."

Activating the ability of Unlimited Blade Works, Ailin instantly absorbed all the experience his "past self" had accumulated through years of dedicated training.