Chakra is a special energy produced by the fusion of spiritual and physical energy in human cells.
From childhood through adolescence, as a ninja's body and mind develop, so does their chakra.
In adulthood, this growth slows, and in old age or under duress, chakra may even wane.
Typically, most ninjas graduate from the Academy at the age of 12—making those formative years critical for growth.
Naruto Uzumaki and Nagato began to harness their powers around that age; within three or four years, they rose to the pinnacle of the ninja world.
But while young Nagato expended much chakra on his Rinnegan—at the cost of his mobility—Naruto, though blessed with tremendous potential, was once hindered by poor nutrition and became known as a scrawny underdog.
Kisame, however, had always stood out from his peers. Despite his low birth, his growth was steady. Had it not been for his status as a third-class commoner, he might have advanced to Chūnin with ease.
At the age of twelve, it could be said that Hoshigaki Kisame's starting point was even higher than that of Nagato and Naruto.
Determined to learn from their experiences and mistakes, he chose a more scientific method of training to fully unlock his physical potential.
That method was fitness.
In the Naruto world, fitness is a relatively common training practice.
For instance, the Land of Lightning (Kumogakure) has the most prominent fitness culture. The streets are filled with dark-skinned, muscular shinobi. The Raikage himself is a fitness fanatic, with barbells and dumbbells even placed in his office.
Konoha also has its own fitness buffs. Might Guy and his father, Might Duy, were known for running hundreds of laps around the village and following that up with thousands of push-ups and kicks.
Kirigakure (the Hidden Mist Village) is no exception. It has a decent-sized gym where many shinobi go for strength training.
In his past life, Kisame had also been a fitness enthusiast in addition to his experience in street fighting. Though in his thirties, he looked like a high schooler—his youthful appearance a testament to his fitness discipline.
There was another reason he embraced strength training.
After devouring the Thunder Sword: Kiba, Kisame realized his body was nearing its capacity. To absorb more of the legendary ninja blades, his body needed to become stronger—much stronger.
So, fitness wasn't optional. It was imperative.
Kisame was resolute. Once he had a plan, he wasted no time acting on it.
Early the next morning, he headed to the village gym, registered at the front desk, and became a long-term member.
The moment he entered the training area, the heavy scent of sweat hit him—an aroma of testosterone and hard work.
The gym itself wasn't fancy—in fact, it was rather shabby. The walls were stained and worn, the lighting flickered, and the equipment was old and rusted. Kirigakure's humid weather didn't help, causing the metal machines to corrode and groan at every movement. Still, the equipment variety was surprisingly complete.
Kisame had started his day with ten eggs and soon dove into his training.
He began with the dumbbell rack. After testing the weight, he grabbed a pair of 50kg dumbbells, laid back on the bench, and skillfully completed several sets of bench presses and dumbbell flyes.
Boom!
Finishing the last rep, he dropped the weights, sat up, and frowned.
He could feel the blood pumping in his chest, a light tearing sensation—but it wasn't enough.
Back in his previous life, bench pressing 50kg was already enough to turn heads in the gym, potentially even win competitions.
But for twelve-year-old Kisame, it was too easy. The workout didn't even make him break a real sweat.
Clearly, he had underestimated his new body by relying too much on his past life experience.
In his previous world, an adult human body had around 30 to 40 trillion cells. In the Naruto universe, a normal human body has around 130 trillion cells—three to four times that. And for monsters like Kisame, probably even more.
With his regenerative abilities, he didn't have to worry about overtraining side effects like rhabdomyolysis.
So, he revised his training strategy:
If it doesn't kill me, I train until it might!
With that mindset, he massively increased his weights and began a second round of brutal training.
In the large, echoing gym, Kisame trained alone, sweating profusely and violently slamming weights as if in battle.
The morning passed in a flash.
"Huff..."
He exhaled deeply, drenched in sweat, and returned home.
His lunch: several pounds of beef, a large bowl of milk, and a healthy serving of vegetables.
Though Kisame's house was run-down, his father had left behind a modest inheritance. Plus, Kisame had worked as a genin for two years, saving up enough from missions to stay well-fed for now.
After lunch, he took a half-hour nap.
In the afternoon, he didn't return to the gym. Instead, he went to a wooded area by the river to train his taijutsu and ninjutsu.
Taijutsu in the ninja world is diverse—ranging from the Strong Fist Style, Gentle Fist, to various chakra-enhanced techniques. But Kisame's style didn't fall into any of those categories.
He decided to integrate the unrestricted street fighting techniques from his past life into his own taijutsu and form a unique system:
Unlimited Body Art.
What is Unlimited Body Art?
Imagine fighting dirty: you spike your opponent's food with laxatives to weaken them, disturb their sleep all night with drums and noise, then ambush them the next day by ramming a truck into their convoy.
That's the idea.
Unrestricted taijutsu is all about real combat. The first instinct is to sneak attack, deceive, and ambush. Shameless? Yes. Effective? Absolutely.
Techniques like throwing lime powder, groin attacks, biting, feinting—Kisame's "Mad Dog Style"—all fall under this brutal art.
He knew that in a world full of political intrigue and blood-soaked backstabs, unconventional taijutsu could become a true trump card.
So Kisame found a thick tree trunk, about the size of a human, and buried it in the ground as a training dummy.
Staring at the stump, he imagined it as the enemy who had murdered his entire clan.
His face turned red. Rage. Hatred. Killing intent—all boiling like a volcano.
"BOIL!"
He roared and launched himself like a rabid dog.
Eye jabs. Nose picks. Groin strikes. Knee smashes. Headbutts. Body slams.
Every savage technique he could imagine was used.
This chaotic fighting style allowed Kisame to enter a state of bloodlust instantly in real battle, channeling a deadly aura that would overwhelm even elite shinobi.
Crack!
Eventually, the wooden dummy couldn't take the abuse and split in half under the intensity of his training.
Kisame clapped his hands, satisfied. Taijutsu training was complete. Next was ninjutsu.
Water Release was Kisame's specialty.
In the entire Naruto universe, only a few could rival him in water-style jutsu—people like Tobirama Senju, Hanzo of the Salamander, and the Second Mizukage.
Swish. Swish.
Standing by the river, Kisame formed hand seals and summoned a translucent blue shark:
Water Release: Water Shark Bomb Technique.
This jutsu forms a high-speed shark-shaped projectile out of water, capable of immense destruction. Kisame could even encase himself inside the water shark to soar through the air.
He did just that.
The shark took flight, carrying him high into the sky, before plunging into the river like a missile, sending up a massive splash.
Back in the water, Kisame felt at peace—as if he had returned home.
He swam freely for a while, then dove deep underwater. With a flick, a lightning-infused shark-tail whip extended from behind him.
Ssshhhk.
Electricity surged. Kisame twisted his body underwater like a monstrous human-shark hybrid—fast, deadly, and graceful.
In water, his power multiplied. Surrounded or ambushed? It didn't matter. He could fight or escape with ease.
This made him realize: to win, he must always fight on his terms.
If the terrain wasn't favorable, he'd create it with Water Release techniques.
He kept training in ninjutsu until the evening.
Kisame also had a curiosity for genjutsu, knowing how powerful it could be for sneak attacks. But despite his efforts, he just didn't have the talent for it.
So he gave up.
Night fell, stars filling the sky.
Kisame emerged from the water, wrung out his clothes, and returned home.
He ate twenty egg whites and some carbs, then crawled into bed, utterly spent.
The next morning.
Kisame woke up, surprised to find that all the soreness from yesterday's brutal training was gone.
Normally, muscle recovery takes at least 24 to 72 hours, depending on the muscle group. But Kisame had fully recovered overnight.
His chest muscles didn't ache anymore.
Looking in the mirror, he noticed his pecs had visibly grown in size.
He was, without a doubt, a once-in-a-generation fitness prodigy.
From that day forward, every time he trained at the gym, he hit every muscle group—even the forgotten ones.
His training intensity increased rapidly, soon surpassing every other shinobi in the gym.
The clang of metal echoed through the air, mixed with low, guttural grunts.
In the corner, Kisame trained alone while a group of Kirigakure shinobi watched from afar, whispering to each other about the monster in their midst.