King Kai's Planet.
"You're Son Gohan, right?"
"Yes, King Kai."
"The Kaio-ken is a technique I personally created. Though it's called a 'fist,' it's really a secret art to amplify one's ki. And since it's a secret art, it naturally has side effects. Use it lightly and you'll be wracked with unbearable pain; push too far and it could cost you your life. Knowing this… do you still want to learn it?" King Kai asked solemnly.
Gohan already knew all about these side effects. What King Kai didn't realize, however, was just how monstrous the Kaio-ken could truly become, because an ordinary person could never push it to its absolute limit. Only a Saiyan's freakishly durable body could endure it, and when that body is pushed to the brink of death and then revived, their power would skyrocket.
In Gohan's mind, Kaio-ken combined with Senzu Beans was practically tailor-made for Saiyans.
"I want to learn it," Gohan said without hesitation. "And I'm confident I can take it further than anyone ever has before."
"Alright. I'll teach you!" King Kai agreed without further hesitation after hearing the boy's resolve.
"Each time you double the Kaio-ken's output, your base combat power doubles as well…"
He began to explain the principles of the technique.
As it turned out, Kaio-ken's essence was to accelerate the speed of cellular division in the body. Each increase in multiplier doubled the division rate again. Normally, cells follow the natural cycle of division, death, and regeneration, but Kaio-ken disrupts that rule, forcing cells to divide again before the previous batch has even died. Because one's strength is tied directly to the body, this forced acceleration naturally boosts combat power, but it also places tremendous strain on the body, bones, and internal organs.
The heart, in particular, bears the brunt of the stress. As the body's "engine," it must pump enough energy to sustain the rapid cell division, which multiplies the pressure on it.
By this point, Gohan had fully confirmed the truth behind Goku's future heart virus.
When Goku was a child, he had drunk the Ultra Divine Water, which carried a powerful toxin. He hadn't been able to fully metabolize it, and a trace remained dormant in his heart. Normally, his ever-strengthening Saiyan body could suppress it completely, but after learning the Kaio-ken, the excessive strain on his heart weakened that suppression.
Even though each Senzu Bean restored his body to full health, the toxin had long since fused with him on a fundamental level. It couldn't be purged.
Then came the Frieza saga. Achieving Super Saiyan, a 50-fold boost in power, became the final straw.
The toxin exploded during the Android saga, triggered when Goku transformed again. Without the special medicine Future Trunks brought back, he would have been doomed.
"To put it simply," King Kai concluded, "you use your own ki to ignite your cells and force them to divide rapidly. That's the principle of Kaio-ken. Do you understand now?"
"I understand, King Kai. You really are brilliant. I never imagined you'd know so much about the human body." Gohan's tone carried genuine respect.
Inwardly, he marveled. This unassuming, rotund little man might not be all that powerful, but his mind was razor-sharp.
"It seems the Dragon Ball world has a hidden truth," Gohan mused aloud. "Never underestimate those who look harmless. King Kai, Majin Buu, Mr. Popo, Zeno…"
Images of those deceptively harmless yet terrifying beings flashed through his mind.
"Now that you know the principle," King Kai said, "I'll teach you how to execute it properly so you can make it run smoothly."
Gohan listened intently, like the model student he was, not blinking once.
King Kai spoke and demonstrated, prompting Gohan to try it himself.
Three hours later…
"King Kai, you'd better step back. This is my first attempt. I'm not sure I can control my ki." Gohan clenched his fists, gathering energy.
"It's fine. Even if you succeed, you won't be able to do me any real harm," King Kai replied with a touch of pride.
Because Gohan had been deliberately suppressing his ki, King Kai had no idea how strong he truly was.
"Heh… you're in for a surprise. Kaio-ken!"
Before Gohan even finished his sentence, the explosion of power erupted.
The tiny, moon-sized planet quaked violently. Buildings collapsed in an instant.
King Kai was blown straight into the lone tree on his planet, clinging to its trunk for dear life.
"Hey, hey, hey! Gohan! Control yourself or you'll destroy my home!" King Kai shouted in alarm.
But Gohan's first activation of Kaio-ken was far too intense to rein in.
Boom! Hum!
His small frame swelled slightly, muscles bulging. His hair stood up just a bit, the usual white ki aura around him turning crimson.
His combat power soared from five million to ten million.
"Triple Kaio-ken!" Gohan roared.
His power shot up again, hitting fifteen million.
"That's enough! Stop! For the love of—!"
"I'm gonna die here!"
"If you die again as a soul, you'll vanish completely!"
The pressure from his ki swept across the afterlife itself, sending ripples of chaos through the entire realm.
Even Hell echoed with the howls of the damned. The queue of souls before King Yemma's desk was thrown into disarray.
Truly, it was a scene that shook heaven and earth and made even ghosts weep.
After all, even fifteen million in combat power at this point in time was beyond monstrous.
"Gohan, stop right now!" King Kai barked.
"But I don't think I've reached my limit yet. I can still go higher!" Gohan protested.
"If you don't stop, my planet will crumble to dust! Can't you hear the wailing from Hell?"
"…Alright." Gohan gradually reined in his ki, letting the Kaio-ken aura fade until he returned to his base form.
"Whew!" King Kai landed, wiping the sweat from his brow.
"Gohan… you never told me you were such a freak of nature. There can't be more than a handful in the entire North Galaxy who could match you," King Kai grumbled.
"You never asked. Besides, I don't think I'm that great in the North Galaxy." Gohan thought of the sealed Majin Buu on Earth. Compared to that monster, he still had a long way to go.
"By the way, Gohan… before you powered up, what was that thing you said about a grandma crawling under the covers?" King Kai asked curiously.
Gohan smirked. "Just a joke."
"Grandma crawling under the covers… that's your idea of a joke?" King Kai blinked, then his face turned red before bursting into uncontrollable laughter. "Hahaha! That's the dumbest thing I've ever heard… and it's hilarious! Hahaha!"
Gohan could only shake his head. He'd never understand why King Kai's sense of humor was so… easy to please.