The next morning, Kai woke up feeling refreshed. He sat up and glanced over at Zhi-Zhi's corner.

The little tortoise was already awake, he was perfectly positioned so his shell gleamed in the early morning light, giving him a dignified and wise look.

I bet he's been awake for hours, trying to get that 'wise old master' effect just right, Kai thought, amused. Did he practice different poses? Test out various angles to catch the light? I can almost picture him shuffling back and forth, muttering about optimal feng shui for maximum sagacity.

"Good morning, Zhi-Zhi," Kai said, smiling. "Ready for some training?"

"A true cultivator is always ready to impart wisdom, young Kai,” the tortoise replied. “I suppose I can spare some time to oversee your training."

"I'm honored by your generosity," Kai said, keeping his face straight with effort. "Shall we head outside?"

As they made their way to the training field, Kai spotted Liu Wei already there, practicing the Swift Wind Step. The young man was dashing back and forth across the field, his movements growing smoother with each repetition.

"Excellent work, Liu Wei!" Kai called out as they approached. "Your control is improving rapidly."

Liu Wei stopped, bowing deeply to Kai. "Thank you, Master. I've been practicing since dawn."

Kai nodded. "Keep at it for now - I'm going to work on a different skill this morning."

As Liu Wei resumed his practice, Kai turned to Zhi-Zhi. "Alright, my friend. Today, we're going to work on defensive techniques. Specifically, my Iron Skin skill."

Zhi-Zhi's eyes lit up. "Ah, now that's a proper technique! None of this dashing about nonsense. A strong defense is the foundation of true power!"

Says the creature with a built-in shield, Kai thought wryly. But he nodded in agreement. "Exactly. And who better to learn from than a master of defense like yourself?"

The tortoise preened at the compliment. "Well, I suppose I could share some of my vast knowledge. What exactly does this 'Iron Skin' technique entail?"

Kai explained the basics of the skill - how it allowed him to reinforce his body with qi, increasing his durability and resistance to damage. "The tricky part," he concluded, "is that to increase my skill, I need to actually take hits while the skill is active."

Zhi-Zhi nodded. "Ah, yes. The time-honored tradition of learning through pain. Very wise."

Easy for you to say, Kai thought. You're not the one who's about to get beaten up.

"So," Kai said, clapping his hands together. "I'm going to activate the skill, and then I need you to... well, attack me."

The tortoise' blinked. "Are you certain, young Kai? My power is not to be underestimated."

"Absolutely,” Kai nodded. “I'm counting on your strength for this. As a Peak Qi Refining cultivator, your attacks will be perfect for pushing my Iron Skin to its limits."

Zhi-Zhi puffed up with pride. "Finally, you recognize my true power! Prepare yourself, young Kai. You're about to experience the might of a superior cultivator!"

This is going to hurt, Kai thought, steeling himself. But pain is just another form of experience points in this world.

This tale has been unlawfully lifted from Royal Road; report any instances of this story if found elsewhere.

"I'm ready when you are, Zhi-Zhi." Kai announced, his skin taking on a subtle metallic sheen.

The tortoise's eyes gleamed with anticipation. Without warning, he charged forward with surprising speed for his stubby legs. His head connected with Kai's shin with a resounding THWACK.

"Gah!" Kai gasped, stumbling back. Even through his Iron Skin, the force of the blow was impressive. Yep, definitely going to feel that tomorrow.

"Ha!" Zhi-Zhi exclaimed, looking smug. "How's that for a wake-up call?"

Kai grinned through the pain. "Excellent start. Keep it coming!"

For the next hour, Zhi-Zhi unleashed a barrage of physical attacks. His lack of agility didn't matter since Kai was deliberately standing still, acting as a willing punching bag. Each impact pushed Kai's Iron Skin technique to its limit, the constant stress forcing it to adapt and grow stronger.

"Adamantine Shell Slam!" Zhi-Zhi cried out, withdrawing into his shell. It began to glow with a soft, golden light before he shot forward like a cannonball, slamming into Kai's midsection.

"Oof!" Kai wheezed, doubling over. His Iron Skin flickered but held. This is exactly what I needed. High-level impacts to really test the technique's limits.

As they continued, Kai could feel his Iron Skin growing more resilient. The impacts, while still jarring, were becoming easier to withstand.

Finally, Zhi-Zhi stepped back, looking slightly winded but immensely satisfied. "Ready for the grand finale, young Kai? I'll show you a true qi technique!"

Kai nodded, bracing himself. This is where the real test begins.

Zhi-Zhi's shell began to glow brightly, the air around him crackled as he gathered his qi. "Celestial Tortoise's Roar!"

A visible wave of qi, far more potent than Kai had anticipated, erupted from Zhi-Zhi's mouth. It slammed into Kai with devastating force, completely overwhelming his Iron Skin technique.

Kai felt the protective layer shatter like glass, the remaining energy crashing into his now-unprotected body. The impact lifted him off his feet, sending him flying backward several meters before he crashed to the ground with a painful thud.

"Urgh..." Kai groaned, struggling to catch his breath. Every part of his body ached, and he could already feel bruises forming.

Zhi-Zhi's eyes widened in shock. He quickly waddled over to Kai, his earlier bravado replaced by genuine concern. "Kai! Are you alright? I... I didn't mean to... that is... oh dear. I may have... slightly miscalculated the power required for a human of your... fragile constitution."

Despite the pain, Kai couldn't help but chuckle at Zhi-Zhi's flustered state. He held up a hand, waving off the apology. "It's okay, Zhi-Zhi. This is exactly what I needed."

Zhi-Zhi blinked in confusion. "You... needed to be blasted across the field?"

Kai smiled but before he could respond, his attention was caught by a notification that had appeared:

Iron Skin has reached Level 4!

Your Durability increases by 40% when activated

New ability unlocked: Iron Rebound - Damage absorbed has a 5% chance to be reflected back at the attacker

"Wait, what?" Kai muttered, momentarily forgetting his pain. "Iron Rebound?"

This is new, he thought, his mind racing. The scroll never mentioned anything about reflecting damage. Is this some kind of hidden ability?

Zhi-Zhi, still looking concerned, tilted his head. "What is it, Kai? Are you alright?"

Kai nodded absently, his thoughts elsewhere. "Yeah, I'm fine. Just... surprised."

Could it be that all skills have secret abilities that aren't known? Kai wondered. Or is this something unique to my situation?

He thought back to the games he used to play, how sometimes skills would evolve or unlock new abilities as they leveled up. But this felt different. The Iron Skin scroll had been quite detailed in its description, and there had been no hint of this reflective ability.

Or maybe, Kai mused, a new idea forming, the system is giving me new abilities based on how I use the skills. I've been using Iron Skin as a punching bag, taking hit after hit. Could that have influenced its evolution?

If this was true, it meant that Kai had even more control over his growth than he'd initially thought. By using skills in specific ways, he might be able to shape their development.

"Kai?" Zhi-Zhi's voice broke through his thoughts. "Are you sure you're alright? Perhaps I really did overdo it with that last attack."

Kai shook his head, focusing back on the present. He gave Zhi-Zhi a reassuring smile. "No, you did exactly what I needed, Zhi-Zhi. In fact, you helped me discover something incredibly valuable."

The tortoise puffed up slightly, curiosity overriding his concern. "Oh? And what might that be?"

Kai patted Zhi-Zhi's shell. "Let's just say that sometimes, pushing past your limits can lead to unexpected breakthroughs. Thank you for your help, my friend."

As they made their way back to the hut, Kai was limping slightly but had a satisfied smile on his face. If this is true for Iron Skin, what about my other skills? What hidden potential might they have?

He knew one thing for certain - he had a lot more experimenting to do.