What if Goku never hit his head when he was an infant?
The whole fabric of the Dragonball Z Universe was set upon Goku's head trauma. Because of this, many events unfolded and he became a hero of all galaxies. The saiyan never realized that all of reality rested upon his life. One day, a mysterious fighter embarked on his time machine, with an unknown reason, to prevent Goku's amnesia from happening, resetting the fabric of the universe…
Many years back, as Goku, or Kakarot, as he was known, flew towards Earth like a fiery comet. Planet Vegeta was in flames, Frieza dominated the galaxy, and yet the Earth sat away from all of the commotion; a perfect escape destination for the young Kakarot. The infant crash-landed in a forest, recovering to carry out his orders: wipe the inhabitants off the planet. Just a few miles nearby, there lived an old martial arts master named Gohan. The old man took the saiyan in as his own grandson and named him Goku.
Goku's saiyan influence caused him to be extremely violent, not listening to a word from his adopted grandfather. On the fateful day, when Goku was near a ravine, he accidentally fell over. Suddenly, the noise of a time machine buzzed, and a stranger stepped out. He easily jumped out of the machine and saved Goku's head. At that moment, all of reality changed. Instead of forgetting his saiyan heritage, Goku, better known as Kakarot, began to carry out his orders to destroy the human race. He posed as a well-behaved child to Gohan, while learning martial arts. When Kakarot's power level reached 11, a full moon rose. With his strength multiplied to 110, Kakarot tore apart Gohan's house, along with the old man, who was powerless to stop him.
As the saiyan boy grew up, he constantly caused destruction. He became known as the "demonic destroyer". When he was of 21 years of age, most of the planet was in ruins. One day, as Kakarot had just finished destroying West City, one of the last places still intact, one human stood against him, his first rebel to his reign of terror. The human was known as Yamcha, with a power level higher than a normal human.
"What is the point to come so far just to destroy?" said Yamcha.
"Ha! Foolish human. Your pitiful attempt to stop me is almost sad," said Kakarot. "You have no concept of my powers, and how I could smash you to bits."
"I don't care if I die here. If I fall, I'm taking you to hell with me! Sokidan!" Yamcha fires his energy, which Kakarot narrowly dodges. A thin cut appeared on his shoulders, skimmed by Yamcha's Sokidan.
"What a joke… a human with energy manipulation. That was enough to graze my shoulder, insect. It seems that there are people who are capable to combat me," said Kakarot.
"Who are you to judge us? Monster you are, you are still just as human as us!" said Yamcha.
"Human? How ill-informed you are, little mouse. I am a warrior from another world, superior to your so-called 'mankind'."
"Another world? What the hell do you mean?"
"It means that I am a saiyan warrior, and you are a human, therefore you do not deserve to live before me! Now be gone!"
Kakarot shot an eye beam at Yamcha, which pierced his heart. He was dead before he hit the floor, stained with blood. The saiyan tyrant's cold demeanor quickly diminished as he realized that there were others who could resist, maybe even stronger than the "Yamcha". Yet he learned that time must move on, it was a long day, he needed rest.
That night, Kakarot had another nightmare, in which he was another man, kind and gentle to the innocent. He was called Goku, his old alias. This Goku helped everyone around him, while trying to find the Dragon Balls with the turquoise-haired lady, Bulma. The whole image caused Kakarot to have a lack of sleep.
As he dreamt, a not-so-old person sat a distance from him, watching him in his time machine pod. Things were going as planned.