(This is my first time writing, so please forgive me if the writing is poor in the beginning. It will gradually get better later.)
Age 740
"Goodbye, Kakarot!"
Bardock pressed his palm tightly against the glass, silently murmuring to himself as he watched Kakarot in the spacecraft.
One year later, Age 741
A spherical spaceship fell like a meteor onto Mount Paozu. An old man discovered the baby inside and gently picked him up.
"From now on, your name will be Son Goku!"
Late Age 748
"Who... who am I?" A crab-haired boy held his head and muttered to himself in confusion.
The crab-haired boy calmed down and looked around at the woods and the house behind him. In an instant, he seemed to remember.
He was both Son Goku and an ordinary young man from Earth-or rather, their souls had fused.
"I never expected to suddenly cross over while watching three generations appear together in Dragon Ball Heroes. No, perhaps it wasn't crossing over." Son Goku stared at the sky, his eyes drifting out of focus.
"I'm neither Son Goku nor Yan Ni. Or maybe I'm both of them! Whatever. From today on, I'm Son Goku, or... Kakarot!"
Son Goku went inside, lay down on the bed, and thought about what to do next.
"It's late Age 748 now, which means there's less than a year until I meet Bulma." Son Goku looked at the calendar on the wall and spoke to himself.
In fact, he had imagined more than once what would happen if he crossed over into the Dragon Ball world.
If he became a Saiyan, there were four things he couldn't do without: Senzu Beans, the Dragon Balls, a gravity chamber, and learning to use ki.
Coming back to his senses, Son Goku looked around. Memories of the past few years came to mind, and his eyes grew moist.
If only it had been a year earlier, maybe Grandpa wouldn't have died.
Wait, it hasn't been a year since Grandpa died. I can use the Dragon Balls to bring him back.
But Grandpa seems to have found love in the afterlife-Fortuneteller Baba. Maybe he wouldn't agree to let me revive him.
"Either way, the first step is to find Grandpa Master Roshi and become his disciple." Son Goku sprang out of bed and stretched his limbs.
He casually picked up the Power Pole from the wall and set off on his journey to become a disciple.
Half a month later, Son Goku floated on the sea, looking at the island ahead. He finally breathed a sigh of relief. "I finally found it!"
Master Roshi was lying in a deck chair, reading a pornographic magazine, a lecherous grin appearing on his face from time to time. Perhaps he was too engrossed, because he didn't notice Son Goku's quiet arrival.
"Hello, Grandpa Master Roshi! My name is Son Goku, and I want to become your disciple!"
The voice that suddenly sounded beside his ear startled Master Roshi into a flurry, and he dropped the pornographic magazine on the ground.
Master Roshi recovered, picked up the magazine and brushed the dust off it, then looked at the boy in front of him.
"You want to become my disciple, and your name is Son Goku. Wait, Son Goku?" Master Roshi pushed up his sunglasses and looked at Son Goku.
"Yes, Grandpa Master Roshi. My name is Son Goku, and Son Gohan is my grandpa," Son Goku told Master Roshi with a broad grin.
Catching sight of the magazine in Master Roshi's hand out of the corner of his eye, he couldn't help thinking that Grandpa Master Roshi was still the same old pervert.
"Gohan's grandson, huh? How has Gohan been lately?" Master Roshi couldn't help recalling his two disciples.
Master Roshi waited a while without hearing a reply. He looked at the crab-haired boy, only to find him hesitating, seemingly unable to get the words out.
"Grandpa... Grandpa died." Son Goku finally said the words he didn't want to say.
Master Roshi froze for a few seconds when he heard that. "Sigh, the dead are gone. Child, you don't need to be sad anymore." Master Roshi felt terrible too, but he still comforted Son Goku.
"Let's not talk about that. You want to become my disciple? You're Gohan's grandson, so I can agree, but my training is very hard."
Perhaps because of Gohan's death, Master Roshi didn't ask Son Goku to bring him a beautiful woman, and became very serious.
"Thank you, Grandpa Master Roshi!"
Master Roshi looked at the sky and saw that it was still morning. He turned to Goku and said, "Since you're becoming my disciple, your training starts today. Come with me."
Master Roshi then took Son Goku to a cliff. He carved the character for turtle on a stone and casually tossed it over the edge.
"See that stone? Find it, and you'll get to eat today. If you can't find it, you'll go hungry." After saying that, Master Roshi walked away without looking back.
Son Goku looked at the familiar scene before him and smiled faintly.
"Okay, Grandpa Master Roshi!"
Five days passed in the blink of an eye. Son Goku could clearly feel himself slowly growing stronger, but unfortunately, that wasn't enough. He needed to get stronger even faster!
Early that morning, after delivering milk, Son Goku went to find Master Roshi. Seeing him reading a pornographic magazine again, he smiled, and an idea came to him.
Son Goku carefully approached Master Roshi and shouted at the top of his lungs, "Grandpa Master Roshi!"
The enormous shout startled Master Roshi right out of his deck chair. He immediately hid the pornographic magazine and coughed twice, putting on a serious front.
"Ahem, ahem. Goku, what is it?"
Son Goku was amused by the sight of the old lecher pretending to be serious, but he held back his laughter. If he laughed, he'd definitely get a beating.
"Grandpa Master Roshi, I want to make my training a little harder. My body has been a little unusual since I was young, and I don't think this amount of training is enough."
"No problem. Starting tomorrow, I'll gradually increase your training. If that's all, go on and get back to it." Master Roshi had actually noticed that Son Goku's body was unusual too.
The amount of training he was giving Son Goku now was the same as what he had given his two disciples, Son Gohan and the other one. They had been exhausted half to death after training, but Son Goku only broke a sweat and panted a little.
Half a year later, in a wasteland, two figures exchanged blows at high speed. To an ordinary person, they looked like two dark shadows colliding nonstop, each impact leaving cracks in the ground.
Master Roshi threw a punch at Goku's head. Goku raised his left hand to block the incoming arm, then gathered a ball of energy in his right hand and hurled it at Master Roshi. Master Roshi instantly moved more than ten meters away.
"Not bad, Goku. In just half a year, you can already fight me to a standstill." Master Roshi had never seen a genius like Goku, who could fight him to a standstill after only half a year.
Son Goku scratched his crab-like hair, smiled, and said, "It's all thanks to your training, Grandpa Master Roshi."
Son Goku had a constant feeling that his talent had become even more terrifying after crossing over. Perhaps his training had increased, but it had only been half a year, and he was already evenly matched with Master Roshi.
His power level might be higher than Master Roshi's, though his martial arts skills were inferior. But this would have been impossible in the original story.
"I don't have much left to teach you. All that remains is for you to hone your martial arts skills. You should also get out and see more of the world. You can never become a martial arts master through training alone." Master Roshi looked at Son Goku, feeling a little emotional.
"Huh? Grandpa Master Roshi, are you sending me away?"
"I'm just telling you to go out and gain experience. Before you leave, I'll give you something-the Flying Nimbus. Of course, whether you can ride it is up to you."
Seeing Son Goku's seemingly reluctant expression, Master Roshi's mouth twitched. This kid really had a huge appetite. It would be good for him to go out and gain experience.
Looking at the Flying Nimbus before him, Son Goku had to admit he was a little nervous. He wasn't the Son Goku from the original story, and perhaps his heart was no longer pure. Whether he could ride it would be down to luck.
With a light hop, Goku landed on the Flying Nimbus.
"Nice! I didn't expect I could still ride it. A half-pure heart counts as a pure heart too, huh!"
Goku was delighted. He had already prepared himself for being unable to ride it.
"Grandpa Master Roshi, could you give me that bead around your neck too?" Goku asked, scratching his crab-like hair.
"You little brat, take it." With that, Master Roshi tossed the bead from around his neck to Goku.
Goku hurriedly caught it, then thanked Grandpa Master Roshi.
Sitting on the Flying Nimbus, Goku got a feel for how to control it, then flew into the distance as a streak of golden light.
"Goodbye, Grandpa Master Roshi!" Goku's voice echoed across the sky.
"Goku, don't forget to enter the 21st World Martial Arts Tournament!"
"Okaaay-!"
(Don't think of the protagonist as Goku from the original story, or as someone who has completely crossed over. He is a new personality created by the fusion of souls. His personality will be a little like the original Goku's, since they fused, but there are still differences.)