Kaio-ken

Son Goku closed his eyes and, following North Kai's guidance, began to perceive the flow of ki within his body.

The circulation of ki... it's not like it usually is. This feeling, it's like igniting all the ki in my body... no, it's stranger than that, like "tightening" the ki?

"First, try the one-fold Kaio-ken." North Kai's voice rang in his ears, his tone uncharacteristically serious. "Remember, you must proceed step by step; do not be impatient. This technique places an immense burden on the body. If you are even slightly careless, you will injure yourself."

Son Goku nodded, carefully guiding the ki within him to circulate along the special trajectory North Kai had taught him.

At first, the flow of ki was somewhat stiff, like a clogged riverbed. But as he continued to try, that ki gradually became smooth, beginning to surge through his body in an entirely new way.

"Hah!"

He let out a low shout, and a pale red aura suddenly erupted around him. Although faint, it was undeniably there.

The fan in North Kai's hand dropped to the ground with a "clatter," his eyes wide as saucers: "Y-you succeeded on the first try?!"

Son Goku felt the surging power within his body, clenched his fist, and a grin of excitement spread across his face: "So this is... Kaio-ken? I feel like my power has indeed increased, but it's not enough!"

"Wait! Don't be rash—"

However, Son Goku had already closed his eyes and begun adjusting the circulation of his ki once more.

I've mastered the feeling of one-fold. So, what about two-fold? Just speed up the circulation of the ki and make that 'burning' sensation more intense... like this?

His aura surged violently, the red flame around him shifting from pale to a vivid crimson, like a raging fire.

"Two-fold Kaio-ken!"

BOOM—!

The ground of King of Worlds Planet trembled slightly, and the dust under ten times gravity was whipped up by this momentum. North Kai was blown back repeatedly by the shockwave, his chubby cheeks fluttering in the wind.

"T-this is only the first day!" North Kai gasped, cold sweat seeping onto his forehead. "Goku! Stop! Your body won't be able to take it!"

But Son Goku did not stop; he felt he could still go on.

He felt the increasingly violent power within him, and a sense of unprecedented excitement welled up in his heart.

I can be even stronger... I can withstand even more! This power... it makes my whole body tremble!

"Three-fold Kaio-ken!"

The red aura grew more intense, Son Goku's hair dancing wildly in the shockwaves, his eyes seemingly burning with fire.

"Four-fold!"

"Five-fold!"

With every increase, North Kai's heart trembled along with it. He looked at the young man before him, as if seeing a monster.

"Six-fold!"

"Seven-fold!"

"Eight-fold!"

Above King of Worlds Planet, the crimson aura shot straight into the clouds, staining them the color of blood. Son Goku's figure flickered within the flames, appearing like a god of war.

North Kai was completely speechless, standing there blankly, his expression shifting from shock to numbness, and then to a kind of near-fanatical awe.

"Nine-fold!"

"Ten-fold Kaio-ken—!!!"

With that final roar, the aura around Son Goku reached its peak. The crimson light all but enveloped him, and the terrifying pressure made King of Worlds Planet tremble slightly.

But just then, Son Goku's brows furrowed slightly.

My body... it's starting to hurt. My muscles feel like they're being pricked by countless needles, and my bones are groaning under the strain... Is this the limit? No, this isn't the limit, I feel like I can hold on a little longer...

He gritted his teeth, forcibly suppressing the tearing pain, and began to move his limbs while in the ten-fold Kaio-ken state.

"Hah!"

"Hyaah!"

Every punch thrown brought with it a piercing sonic boom. Every kick left a crimson trail in the air. He darted and weaved under ten times gravity, his speed so fast that even North Kai could barely track him.

Watching this, North Kai muttered to himself: "A monster... this kid is simply a monster... no, 'monster' isn't enough to describe him..."

Ten minutes later.

"Huff... huff..."

Son Goku finally stopped moving, his forehead covered in beads of sweat. He felt the tearing pain inside him growing more intense, knowing that if he continued, his body would truly give out.

"Release!"

The crimson aura dissipated instantly, and Son Goku let out a long breath, his legs turning to jelly as he nearly collapsed to the ground. He quickly braced himself with his hands on his knees, gasping for air as sweat dripped onto the cracked surface of King of Worlds Planet.

That was close... ten-fold is indeed the limit I can use within the safety range. If I increase it any further, my body will truly collapse. But... this power is truly fascinating. It's a shame that Kaio-ken is a 'three-second hero' technique; it's destined to be used only as a trump card.

North Kai hurried over, his expression extremely complex, filled with both worry and undisguised surprise: "Goku... are... are you alright?"

Son Goku looked up and grinned, and though his face was pale, his eyes remained as bright as stars: "I'm fine! Just a little tired. Lord Kai, thank you for your guidance!"

North Kai looked at him, sighing after a long moment before revealing a gratified yet slightly helpless smile: "Goku, you're too polite. To be honest, I've had many disciples over the years... no, in all my long life, I've never seen a genius like you. It seems my ultimate technique, the Kaio-ken, will be carried to new heights in your hands."

Son Goku scratched his head bashfully, his tail swaying gently behind him: "It's all thanks to Lord Kai's teaching."

"No, no," North Kai waved his hands repeatedly, his expression turning serious. A rare look of gravity appeared on his chubby face. "It is your own talent, strength, and comprehension that have allowed you to push the Kaio-ken to this level. If it were anyone else, even if I taught them hand-in-hand, they could never reach this point on the very first day. You brat... just what kind of potential is hidden inside your body?"

Son Goku merely smiled, offering no answer.

Ten-fold Kaio-ken... it is still not enough. On Namek, facing those true monsters, I must become stronger. But at least, now I have a trump card.

Over the next few days, Son Goku continued his training on the King of Worlds Planet, consolidating his mastery of the Kaio-ken.

By incorporating the Senzu Bean, the time Son Goku spent improving his control over the Kaio-ken was greatly reduced. To avoid irreversible physical damage, he limited his consolidation of the technique to ten-fold.

North Kai watched him practice repeatedly under ten times gravity—from one-fold to ten-fold, then deactivating, then restarting—his movements becoming increasingly proficient. His heart was filled with both gratification and worry.

"Goku," two weeks later, North Kai called out to Son Goku, who was resting. His expression was uncharacteristically stern. "You have mastered the Kaio-ken well enough. But I am going to teach you one final technique, my greatest trump card—the Spirit Bomb."

Son Goku's eyes lit up, and his tail stood straight up. "Spirit Bomb?"