The rest of the group were trying to catch Bubbles, Piccolo included. Because the gravity was too much for them, except Piccolo and Goku, the rest did not wear their weighted clothes. King Kai had told them the gravity was 10x Earth's gravity, which amazed them even more, that the Saiyan's home planet actually had such a high gravity.
"Hey! Piccolo, what do you think you're doing?! You're not allowed to train with them before you pass my test!" King Kai rebuked.
"Hmph! I don't need your lousy training!" Piccolo gnashed his teeth and left. He walked up to a tree and sat down cross-legged and started meditating.
"Come on, Piccolo. It's not hard." Goku saw everything, he walked up to Piccolo, and tried to encourage him to continue telling jokes to King Kai.
"I do not need to humiliate myself!" Piccolo yelled angrily, his face flushed from remembering his attempts at telling jokes to King Kai.
Goku tried persuading Piccolo several times but failed. Without a choice, he walked up to Raditz and asked his big brother to help.
"Goku is really too kind... He's helping his archenemy to get stronger..." Krillin looked speechlessly as Goku was begging Raditz to persuade Piccolo.
"You do realize Piccolo still wants your life, right?" Raditz was also speechless. Although he knew that Piccolo would become good in the future, Goku did not know that yet. But he still treated Piccolo like a friend already.
"Don't worry! I'll just have to defeat him!" Goku said confidently.
"Is this how he made Piccolo turn good...?" Raditz wondered in his mind. To treat his enemies as friends, if it works, he will convert his enemies into friends. But Goku was doing it unwittingly, this was his nature, and not done with ulterior motives.
"Alright, I'll try." Seeing how Goku was practically begging him, Raditz nodded and walked up to Piccolo.
"Hey, are you really going to give up training?" Raditz asked Piccolo.
"I don't need to humiliate myself to get stronger, I can train by myself!" Piccolo looked sternly at Raditz.
"All it takes is a bit of humiliation for you to give up strength. If you're fine with the humans getting stronger than you, if you're fine being dead last of the rest of the group. Then suit yourself." Raditz pressured Piccolo with his Ki.
"... I tried." Piccolo said silently. He had a really thin skin, otherwise, with how competitive he is, there was no way he would simply give up his training with King Kai.
"Yeah, I know. I don't have a 'great' sense of humor either. So why don't you just look up a joke from the gag book, I'm sure he'll laugh in no time." Raditz gave a piece of advice to Piccolo, he pointed at the book on the table, next to King Kai, who was reclining on the chair.
A few days later, King Kai announced that Piccolo passed his test. Unknowingly, Piccolo had surreptitiously memorized a few jokes from the gag book while King Kai was out driving on his car.
At first, Piccolo simply extended his arms to catch Bubbles, but after getting berated, as this action did not help him train in King Kai's 10x's gravity. He finally obediently chased after Bubbles, with Goku close to catching Bubbles, Piccolo unrelentingly pushed harder, which in return made the rest of the group work harder, their hard work pleased King Kai.
Four months later, Raditz finally managed to learn Kaioken, unfortunately, comparison made one despair, Goku took 2 months to catch Bubbles and hit Gregory with the heavy hammer. And in simply another 2 months, he learned Kaioken. Yet it took Raditz twice the time to learn the same technique.
"Shit! Is this the main character halo? Or is Goku just so talented?!" Raditz grumbled in his mind. If his talent was half of Goku's, then everything he did, required twice the effort to catch up with Goku, who is now his younger brother.
Piccolo, although stronger than the rest of the group, he did not have the same talents as a Saiyan. It took more than 3 months for him to catch Bubbles and hit Gregory with the heavy hammer. The rest of the group had already caught Bubbles, but was still nowhere close to hitting Gregory.
Instead, they had hammered King Kai's planet into a beehive, large sized indents littered the whole planet. King Kai regretted making the 2nd challenge hitting Gregory with a heavy hammer.
What was surprising was that Gohan did not fall behind the group of humans, he did quite well for just having started learning martial arts 4 months ago. Although he was still weaker than Yamcha, he was catching up at a quick pace, he was already as strong as Chiaotzu. Everyone praised Gohan's talent, he was a natural martial artist.
8 Months passed, Raditz and Goku had learned Spirit Bomb, while Piccolo and Tien Shinhan had learned Kaioken.
"How come Spirit Bomb is even harder!" Raditz complained silently. Goku learned Spirit Bomb in 2 months, meanwhile it took Raditz 6 months. Comparison really made one despair... If it wasn't because Spirit Bomb was such an amazing attack that even killed Kid Buu, Raditz would not had put so much time just to learn this technique.
Luckily, Saiyans were talented in energy manipulation, otherwise, he would be like Piccolo and the rest, who did not manage to learn Spirit Bomb. Even just the Kaioken was a big hurdle for the group. Gohan was really talented, but unfortunately, his martial arts experience was lacking, otherwise he would be the next to have learned Kaioken. But thanks to King Kai's extra care, Gohan's martial arts foundation is very sturdy now.
Boom! Boom! Bang! Raditz and Goku clashed continuously in the air above King Kai's planet. After several minutes, the two of them landed on the ground.
"Hehehe, I've improved by a lot, right?" Goku smiled cheekily.
"Yeah. Too much though..." Raditz mumbled. He used to be so much stronger than Goku, but now the two of them were almost equal.
"Are they even humans?" Yamcha mumbled, the aftermath of the clashes earlier had almost sent the group flying.
"They are Saiyans... Sigh..." Krillin corrected Yamcha and looked enviously at the Raditz and Goku.
"Hmph! I won't lose!" Piccolo clenched his fist hard. He had sparred several times with Goku, during these months, but each time, the gap between them grew wider and wider.
"At least you did not feel the same despair I do..." Raditz looked at Piccolo's fist and said quietly in his mind. He had had a much higher battle power that Goku a year ago, but now, the difference between them wouldn't be more than a thousand battle power. The two of them did not experience any Zenkai during their training with King Kai, but Goku improved faster than Raditz, mastered the techniques faster than him, each and every time. Raditz was worried he would be left behind soon, with the rate Goku improved. He didn't have the main character halo, he wasn't especially talented, he was just a normal guy, who happened to take over Raditz' body.
King Kai, like usual, forgot to calculate the group's time spent on returning, luckily, Raditz and Goku were a lot stronger than Goku was in the story, when he rushed back to Earth in haste.
"We'll go ahead." Goku said to the group and powered up, his Ki flared high up in the air and he flew toward the Snake Way. Raditz also powered up and flew away, Piccolo did not want to lose and followed the two.
"Let's follow them!" Gohan said and flew after the three.
"Let's go!" Krillin, Yamcha, Tien Shinhan, and Chiaotzu also followed.
"Damn it! Kaioken!" Piccolo saw the distance between him and Goku and Raditz increase, his Ki was lower than the two in front of him. He could only resort to Kaioken to follow them. His Ki shot up by 50% and he hurried after Goku and Raditz.
"Tien Shinhan, are you also going to use Kaioken?" Krillin wondered. The only way for Tien Shinhan to catch up to the three in front, was to use Kaioken like Piccolo did.
"No. My mastery of Kaioken is too low, I'm afraid I won't be able to battle once I reach Earth if I use it now." Tien Shinhan shook his head. What use was it for him to use Kaioken now, if it would leave him incapacitated for the battle ahead.