Reincarnated as the third son of the Duke

"Those who lack an understanding of the essence of sword techniques believe that mana must be distributed separately for each movement."

Aizen spoke as he gently ran his fingers along the wooden sword, his gaze fixed on William.

"When striking forcefully, they focus solely on their arms. When clashing blades, they concentrate only on pressing down with weight. When evading, they channel everything into their legs. Their mana surges wildly with every motion."

William hesitated before responding.

"...Is that incorrect?"

"Of course it is."

The immediate reply made William instinctively shrink back. In his past life, he had wielded his sword exactly as described. Hearing such a firm denial filled him with embarrassment.

"Then how should mana be utilized?"

"Like this."

Whoosh.

Aizen swung the wooden sword through the air. A bluish energy emanated from his body, forming a visible aura.

William flinched at the sight.

"Unbelievable. He materialized his entire body's mana without any warning."

Typically, even renowned knights could only manifest their mana briefly at specific points of impact when unleashing their strength. Yet Aizen had effortlessly shaped his entire body's mana merely to serve as an instructional aid.

"Watch closely."

As Aizen moved, the materialized mana shifted fluidly with him, altering its form in accordance with his posture.

The intricate details of mana circulation became evident—how it flowed through the body with each stance, where it should be concentrated during moments of instantaneous change. Everything was laid bare before William's eyes with striking clarity.

Entranced by the near-supernatural display, he realized only belatedly that the demonstration was nearing its end.

"Do you understand?"

"P-please, show me once more."

"As many times as you need."

Aizen smiled at William's eagerness and repeated the demonstration.

William's eyes darted rapidly, tracing the movement of mana. Each motion—seemingly effortless—was a priceless treasure, worth more than gold.

"How about now? Do you grasp it?"

"...The mana remains evenly distributed throughout the entire body."

"Yes. Exactly that."

Aizen's lips curled into a satisfied smile at his perceptive student.

"If one redirects all their mana to different parts of the body with each stance, significant gaps will appear between movements. Once a technique is executed, the flow will inevitably break. And in battle, even the slightest hesitation can cost a warrior their life."

William was left speechless.

He had always believed that swordsmanship was about minimizing those gaps as much as possible. But now, he realized—the true mistake was allowing those gaps to form at all.

It felt as if he had spent his life tirelessly digging into solid rock, convinced it was a gold mine.

"No wonder knights are so quick to assume proper stances," he thought to himself.

"When using mana, one must maintain reinforcement throughout the entire body while still reserving enough for redirection. The key is not to withdraw mana from where it is already deployed, but rather to continue swordplay using the residual mana that remains."

Aizen momentarily paused before retracting his materialized mana.

This time, he assumed a proper stance.

"Once mana control reaches its peak, one can achieve feats like this."

Boom.

As he swung the wooden sword, the very air around it ruptured with a deafening impact.

William's eyes widened in shock, but the true astonishment came a moment later.

Boom. Pop. Boom.

"What... is this?!"

The sword flowed.

Ordinary swordsmen had to forcefully cleave through the air with each strike to produce even a fraction of that sound.

Yet Aizen, without pausing his fluid movements, was still managing to rupture the very atmosphere.

Even as he witnessed it, William found it impossible to believe.

Aizen gracefully danced with the wooden sword, executing his tenth strike before lowering his hand.

"This is the swordsmanship you shall learn from now on, Third Young Master."

William swallowed hard.

Aizen had not even revealed the Lionheart Sword yet. He had merely demonstrated the outcome of supreme mana control.

And yet, even without utilizing a true sword technique, the sheer force of this mastery was overwhelming.

For the first time, William truly understood just how vital a teacher was to a swordsman.

As he stood in awe, a thought crossed his mind.

"...Then what happens when the Lionheart Sword is used in a state of perfect mana control?"

Hearing the question, Aizen let out a hearty laugh.

"Naturally, the power would be tremendous. If possible, I would show you myself... but this is not the place for it."

"Why not?"

"This training ground is shared by other knights. If I unleashed that technique here, I would be scolded by the Grand Duke himself."

That explanation was more than enough.

If used properly, the technique could obliterate the training grounds.

"Now that you know the path forward, let us begin refining your mana control. We will start with transitioning between vertical and horizontal strikes."

It was not merely about swinging the sword—it was about maintaining a constant flow of mana throughout the body.

Whoosh.

"I thought it would be easy, but my old habits keep getting in the way."

Though his body had changed, his soul had spent a lifetime repeating the same motions. The muscle memory from his past life often resurfaced, causing him to revert to the habit of executing rigid, broken strikes.

It had become an almost reflexive action, making it all the more difficult to correct.

"You're improving significantly. You learn quickly."

"Thank you."

Despite Aizen's praise, William found no reason to smile.

Having wielded the sword for over a decade in his past life, he had assumed that mastering this technique would take no more than a single day.

Yet, it had taken him three entire days just to unlearn his old habits.

"For now, I must focus entirely on swordsmanship. If these old habits resurface at the wrong time, it could cause unnecessary trouble."

If his technique had been sloppy, it would have been easier to discard. But even with its flaws, his swordsmanship had become a distinct, recognizable skill.

If he inadvertently displayed such an advanced technique before others, he would draw unwanted attention.

To avoid suspicion, he had no choice but to fully reconstruct his approach.

"Well, at least it worked out in my favor. My progress appears fast for a beginner, but not suspiciously so. If I had looked too polished, it would have raised questions."