Beerus' dad had a child with a universe 7 saiyan, but Zeno destroyed them both for committing an act of taboo. They named the child 'Alpha', because they knew he would be the strongest.
When Chiaotzu, Tien, Yamch and Piccolo died, they all found their way to King Kai. Piccolo got an extra year on there than the others, so when they got there, Piccolo had passed all the trials and was learning the Kaioken. By the time he was brought back, he had it figured out. But he hadn't grown powerful enough to match Frieza.
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When Piccolo regains consciousness he's lying in blue grass. The water and sky is green and he is on Namek. "Namek... I can sense so many powerful energies. There's a Namekian over there. I should check it out." He goes over to Guru's house.
Nail steps out of the house and sees Piccolo coming. "Halt! I didn't think there were any namekians left. What is your business? Lord Guru's time of passing has come."
Piccolo tries to explain. "I'm here to stop Frieza, but I need to get more powerful. I was thinking that I could have my potential unlocked by Lord Guru. My father told me about it," he says.
Nail lets him inside and Piccolo meets Lord Guru. "Very well young one. I shall unlock your hidden potential. But I must warn you, it will not be enough to defeat Frieza." He places his hand on Piccolo's head and a white light engulfs him.
"You're right. I'm still not strong enough. I'm not even as strong as the namekian over there," Piccolo says.
Nail has a thought. "There is a way. A forbidden ritual to make a namekian far stronger. Namekian fusion. Two namekians can merge and become much stronger than just their powers added together. May we try that Lord Guru?" Guru nods, so Nail instructs Piccolo on how to do it.
"Yes. Like that. Now, fusing!" he shouts, becoming a bright light that goes into Piccolo. Piccolo stands up and looks at his hands.
"My god... this is incredible! With this, I can beat Frieza! But... Nail is sad that you are dying, Lord Guru. Thank you."
Guru stops him. "Wait. I am dying and have nothing left to give to this world. So before I die, I might as well sacrifice myself for Namek. Merge with me too. You will get a smaller bossy than with Nail, but you will have my wisdom," he says.
Piccolo agrees and they fuse. He is now more powerful than before and has yellow patches instead of pink, even though he hasn't actually aged.
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"Incredible! I know so much and have so much power! This weighted clothing doesn't really feel like anything anymore. Maybe I should make it heavier. 30 tons should do the trick. Now I should go help Goku and the others." He flies off.
