Naruto: Aizen's Shadow in Konoha

Limited by the environment, Aizen lacked the abundant water resource present during his fight with Minato. He was forced to condense chakra within his throat, expelling a swirling torrent of water to form a defensive barrier.

A hissing roar filled the air as the scorching flames collided with the icy water wall, instantly generating a cloud of dissipating steam. 

Nawaki's face paled, mirroring the shock of a man who'd just lost his greatest treasure. Though his parents were long gone, the emotional impact remained.

He'd unleashed his trump card, the B-rank Fire Style: Extinguishing Flame, a jutsu originally intended for Namikaze Minato. Its power was undeniable. Yet, Aizen had effortlessly countered it. 

It needs to be emphasized here, in the Naruto world, jutsu are classified into five categories: D, C, B, A, and S. While the higher the rank, generally the stronger the jutsu, this isn't always a rigid rule.

The ranking primarily reflects the difficulty of learning a jutsu. After all, if a jutsu offered immense power with minimal learning complexity, who would bother mastering advanced techniques? The system would lose its purpose.

That said, a higher rank typically indicates greater potential power. It's a general guideline for jutsu effectiveness in the hands of a competent ninja.

For example, Uchiha Madara's masterful use of the B-rank Fire Style: Extinguishing Flame elevated its power to rival some S-rank jutsus.

S-rank jutsus, also known as Mystery-level jutsus, are the pinnacle techniques wielded by Kage-level powerhouses. Some S-rank jutsus are classified as Forbidden Techniques due to their inherent risks to the user, but their power remains undeniable.

The gap between S-rank jutsus can be vast. Take offensive jutsus: Raikiri, the evolved form of Chidori, and the Wind Style: Rasenshuriken are prime examples. Similarly, Lightning Style: Kirin, and the Eight Gates techniques like Night Guy fall under the S-rank category.

The most extreme examples include techniques like Dust Release,and Wood Release: Wooden Golem – all classified as S-rank.

This highlights the immense disparity within the S-rank category, arguably the most unpredictable power system in the Naruto world. The Six Paths power, which comes after S-rank, offers a more defined power structure in comparison.

Despite the ranking system, jutsu effectiveness depends heavily on the user. Aizen's previous Water barrier wasn't used to its full potential against Minato. Similarly, the Water Barrier he used earlier was a weaker version, only strong enough to deflect shuriken. This time, however, he pushed himself, using nearly half his chakra to create a powerful Water Barrier.

Ignoring his own chakra depletion, Aizen focused on Nawaki's defeated expression. With a smirk, he unleashed another jutsu:

Water Style: Water Rush!

He aimed to exploit the water environment created by the Water Barrier for his advantage.

A powerful current surged towards Nawaki, snapping him out of his despair. Unlike Minato who was caught off guard before, Nawaki had time to react due to their earlier exchange. He quickly formed a hand sign and countered with a jutsu.

Earth Style: Earth Formation Wall!

The water slammed into the earth wall, overflowing the top and flooding the area behind it. Nawaki, quick on his feet, leaped to the wall's summit just in time.

This sequence of events had drained both his stamina and chakra reserves. The earlier taijutsu duel with Aizen had taken its toll, followed by the chakra-intensive Fire Style: Extinguishing Flame, which consumed nearly 70% of his chakra.

It's worth noting that while Aizen also expended a significant amount of chakra resisting the flames, the water element has a natural advantage over fire, leading to slightly lower chakra consumption on his part. By the time he extinguished the flames, Senju Nawaki was left with less than 10% chakra.

Furthermore, keeping up with Aizen's exceptional reflexes in their physical confrontation had forced Nawaki to exert even more energy. Blinded by his desire to prove himself, he channeled everything into the Fire Style jutsu, leaving himself depleted.

Now, after weathering Aizen's water surge, Senju Nawaki was finally at his limit. Exhausted, he half-knelt on the wall, gasping for breath.

There was no respite, however. Before he could catch his breath, several high-pressure water jets erupted from the stream, disintegrating the earth wall and sending Nawaki plummeting into the raging water.

He sank, his body wracked with pain. Blood streamed from a wound on his right shoulder, coloring the water red. The injury, coupled with chakra depletion and the suffocating current, blurred his vision and threatened to drag him unconscious.

"Is this it?" he thought weakly. "Maybe death wouldn't be so bad – no more pressure, no more responsibilities, just a chance to finally rest. But… my parents died on a mission, and now I'm leaving too. Tsunade… she must be heartbroken and alone."

With a flicker of his eyelids in the murky depths, Nawaki saw a familiar figure…

"Aizen? Is he here to save me? But why…?"

Just as darkness threatened to engulf him, Aizen dove into the water, grabbed Nawaki, and pulled him upstream.

After what felt like an eternity, Nawaki regained consciousness to a warm sensation spreading through his body. His clouded mind cleared slightly.

"You're awake, take it easy. I'm healing your wound now," a gentle voice soothed. Nawaki blinked, his eyes filled with confusion.