Sasuke understood the logic laid out in the texts.
Fire Release techniques were, at their core, the act of shaping neutral chakra and binding it to a fire nature before release. Repeated use and mastery of enough fire techniques naturally refined that nature transformation over time. Some advanced techniques went further, layering form change on top of nature change. Fireballs compressed into dragons, phoenixes, or spiraling arcs of flame, concentrating heat or widening the area of effect.
But was repetition the only path?
Given his current limits, training nature transformation the way Naruto had was inefficient. Relying solely on repeatedly casting techniques wasn't much better. His chakra was already stretched thin across shadow clones, taijutsu, genjutsu, study, and recovery.
Sasuke shifted his thinking.
Fire's defining trait wasn't flame. It was heat.
And heat, stripped of mysticism, was motion.
In his previous life, temperature was explained as the intensity of microscopic movement. Faster motion meant higher heat. Slower motion meant cold.
Friction creates heat.
That idea lingered.
He gathered chakra into his palm again. He didn't know what chakra was made of, whether it had particles or structure in any scientific sense. That didn't matter. He didn't need certainty. He needed a model.
Within the gathered chakra, he exerted fine control, forcing countless tiny streams to move, collide, and churn against one another. Not violently. Steadily. Like controlled turbulence.
He pressed his palm to the kettle.
This time, steam rose almost immediately. The water inside began to boil in earnest.
It worked.
The satisfaction lasted only a moment. Sasuke withdrew his hand and steadied his breathing.
At normal pressure, water boiled at a hundred degrees. Enough to injure a civilian. Meaningless against a shinobi. This method alone would never be decisive in combat. Increasing the internal motion further might push it higher, but that would demand even finer chakra control.
Still, it opened a second door.
If he applied this principle when releasing fire chakra from his lungs, accelerating internal motion before ignition, techniques like the Great Fireball would burn hotter and travel faster. There was risk. Too much instability could damage his own body.
Problems revealed themselves as soon as solutions appeared.
That was fine.
Finding flaws meant he was thinking clearly.
Sasuke closed his eyes, committing the day's conclusions to memory. As always, he wrote nothing down.
Later that night, long after the compound had gone quiet, he laid out a mat on the tatami and lowered himself onto it.
He moved slowly through a sequence of poses. Palms planted. Spine extended. Breath drawn deep, then released in measured rhythm. Each motion flowed into the next, controlled and deliberate.
Meditative practice.
It wasn't native to this world, but the body understood it anyway.
The exercises loosened his muscles, eased accumulated strain, and calmed his thoughts. More importantly, they sharpened his awareness. His breathing steadied. His mind cleared. Chakra flowed more smoothly when he rose again.
He didn't know if this discipline shared roots with chakra itself.
He only knew that it worked.
And that was enough.