In the cool shade of an early morning, Saitama and Sai stood within the confines of the Sacred Order’s armory, a vast hall lined with ancient and modern weapons alike. Sai’s gaze swept across the rows of gleaming metal and polished wood, each piece holding a story, a purpose.

Saitama, clearing his throat, caught Sai’s attention. “Before we begin, it’s crucial you understand the fundamentals of what we do here and what you are,” he stated bluntly, pulling a small object from his pocket and flicking it into the air. It was a crystal that shimmered with a soft, inner light. “This is Divine energy in its condensed form. We use this to fight, to protect, and sometimes to heal. It’s the core of our power.”

Sai’s eyes were drawn to the crystal, his curiosity piqued by its pulsating light. “And this works against Nightmares?” he asked, his voice filled with a mix of wonder and anticipation.

“Yes, and it’s also effective against anything tainted by Curse energy, including you, since you’re a Cursed Vessel,” Saitama replied sharply. “Your existence is both a weapon and a liability. Here, you’ll learn to control that, to harness it instead of letting it dominate you.”

Sai nodded, the weight of his unique nature settling in—a daunting yet empowering realization.

Saitama, stepping forward, led Sai to a particular section of the armory where rows of sacred tools were meticulously displayed. “These aren’t just weapons,” he said gruffly, “they are extensions of our will, fused with Divine energy. They’re critical to our fight.”

Sai’s attention was captured by a specific weapon, a sleek, black steel three-section staff that seemed to call out to him. Driven by an instinctive pull, he reached out, his hand closing around the staff. It felt right, a natural extension of his own limbs.

(“This one... It feels... right.”)

“Ah, the Dancing Dragon,” Saitama observed, his tone dry but with a trace of approval. “A versatile weapon, and it seems to have chosen you as much as you chose it.”

He led Sai back into the open training field, ready to delve into instruction. “Now, pay attention to the Conduit technique. It’s essential for all exorcists. This technique enables you to draw out your sacred tool’s power, enhancing both the weapon and its wielder.”

Demonstrating, his own weapon—a wooden katana—began to glow with a faint light. “Channel your will, your spirit, into the tool. Merge its energy with yours. That’s how Conduit works.”

Sai attempted to mimic the stance, initially feeling awkward. Gradually, warmth spread through his palms, and the staff began to vibrate with energy, a reaction that caught him off guard.

“Good,” Saitama said curtly. “It’s responding to you. That’s the first step. Mastery, however, will require time and persistent practice.”

Saitama’s expectations were clear and uncompromising. “We’ll have weekly sessions. Each time, we’ll push further, building on what you’ve learned. I don’t expect perfection, Sai, but I demand complete commitment.”

With these stern words, Sai understood the rigors ahead. Saitama’s harsh and blunt approach was not meant to intimidate but to prepare him for the realities of their grim conflict.

A week later. The training grounds were quiet, save for the shuffle of feet and wood clashing against metal. Sai wielded the Dancing Dragon with a newfound finesse, his movements a blend of grace and power.

Ever the stern mentor, Saitama watched from the sidelines, arms folded, his expression unreadable behind the smoke of his cigarette. He flicked his cigarette to the ground, crushing it underfoot as Sai completed another set of maneuvers.

“Not bad,” Saitama grumbled, though the slight nod that accompanied his words was as good as high praise from him. “But don’t get cocky. Mastery isn’t achieved in a few weeks.”

Sai, catching his breath, his chest heaving. “I understand, Captain.”

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(“But why is he so hard on me? I feel like I’m doing double the work compared to everyone else.”)

Saitama’s gaze lingered on the horizon, his mind wrestling with the orders from Yasuko to push Sai harder than the others. He sighed, a rare sign of resignation. “You’re not just anyone, Sai. You’re a Cursed Vessel, remember? You have abilities that could surpass even the best of us if not properly honed.”

Sai narrowed his eyes, trying to gauge whether the harsh training was a form of hidden concern. “So, this is your way of looking out for me?”

“Don’t flatter yourself, kid,” Saitama shot back quickly, his usual gruff demeanor returning. “It’s my job to make sure you’re more than ready. The threats we face... they won’t care about fairness or whether you had a hard day.”

The air grew thick as Sai absorbed his mentor’s words, understanding the harshness as a disguise for deep-seated responsibility. He nodded, setting his jaw. “Alright, Captain. What’s next?”

Saitama pointed towards a row of wooden dummies. “Focus your attacks. Let’s see if you can take them down without burning the whole place down.”

As Sai positioned himself, channeling his energy into the Dancing Dragon, Saitama continued, his voice low. “Remember, it’s not about overwhelming power. Precision, control, understanding the nature of your energy... that’s what separates the reckless from the true wielders.”

Sai unleashed a series of strikes with a deep breath, each accompanied by a burst of dark energy that struck the dummies with pinpoint accuracy. The power he commanded was raw but refined under Saitama’s relentless training regime.

As the last dummy toppled, Sai stood amidst the wreckage, breathing heavy but steady. He looked over his shoulder at Saitama, a silent question in his gaze.

Observing the controlled display of power, Saitama was unfazed. “Good. You’re getting there. Next week will be different.”

As the mist still clung to the grass of the training grounds, Saitama stood facing Sai, his expression more serious than usual. The air was charged with a palpable tension, the kind that precedes a significant test or revelation.

“Today, we take your training a step further,” Saitama announced, his voice cutting through the quiet like a blade. He drew his wooden katana, the movement so swift it was almost a blur. “You need to understand what it means to fight someone who can match and exceed your abilities.”

Sai, gripping the Dancing Dragon tightly, nodded. He knew this day would come when Saitama would truly challenge him, not just as a mentor, but as a formidable opponent.

(“What is his plan? Something doesn’t feel r...")

Without warning, Saitama lunged forward, his attack a direct thrust aimed at Sai’s midsection. Sai managed to deflect it, but only just. The force behind Saitama’s strike was a clear message; this was no ordinary sparring session.

“Don’t hold back, Sai. Your ability to regenerate is your safety net. Still, it won’t help you if you can’t keep up,” Saitama barked, as he unleashed a flurry of strikes, each precise and forceful.

(“Wow, captain’s fast.")

Struggling to keep pace, Sai felt the wooden blade sting across his arm. Almost instantly, the wound began to close up, his skin knitting together as if nothing had happened.

(“It’s working.")

He glanced at the healing wound, then back at Saitama, who was already preparing for another attack.

“This is not just about regeneration. It’s about resilience, anticipation, reaction!” Saitama shouted, each word punctuated by a strike that Sai barely blocked.

(“So, this is the power of Captain Saitama.")

The Saitama’s movements were a lesson in efficiency and skill, honed through decades of combat.

Saitama’s next move was a scheme; he aimed for Sai’s left but switched to the right at the last moment.

(“What? How did he?...”)

Sai was caught off guard and felt the impact against his ribcage. Pain flared, then subsided as his body immediately began to heal.

“See? You heal, but you also need to learn to avoid damage in the first place,” Saitama explained, stepping back to give Sai a moment. “Your enemies won’t wait for you to recover.”

(“He’s right, I gotta get faster!”)

Sai, breathing heavily, adjusted his grip on his staff. “Again,” he said, determination in his voice.

Saitama nodded, and the dance continued—attack, defend, regenerate. Sai’s movements became more deliberate with each cycle, and his blocks became more timely. He was learning to read Saitama’s body language, anticipating rather than reacting.

As they moved, it was clear that despite his age, Saitama possessed a mastery of movement that Sai could only aspire to. His attacks were physical and psychological, testing Sai’s endurance and willpower.

After several intense minutes, Saitama halted, sheathing his weapon. He looked at Sai, who was panting but upright, his earlier wounds fully healed.

“You have the gift of regeneration, but don’t let it make you complacent. In battle, every moment counts, and recovery is a luxury you may not always afford,” Saitama advised, his tone softer now.

Sai nodded, absorbing the lesson. “Thank you, Captain. I understand now—this is about more than just surviving hits. It’s about not taking them at all.”

Saitama’s eyes crinkled slightly, a sign of approval. “Exactly. And remember, Sai, the true test of a warrior is not how fast they can heal, but how effectively they can prevent damage, and how resilient they are under pressure.”

As they walked off the field together, Sai felt a renewed respect not only for his own abilities but for the older exorcist who, with every punishing lesson, was preparing him for the realities of the world they defended.