One of King Kai's darkest theories about how Demon King Piccolo truly turned to evil despite his understood origin is actually proven by the creation of Majin Buu's truth wrathful counterpart in Dragon Ball. Even though Demon King Piccolo was created from the evil in the Nameless Namekian Warrior, and the warrior's goodness formed Kami, King Kai is never convinced that Demon King Piccolo was the byproduct of that split.

After the devastation caused by Vegeta and Nappa's attack on Earth, the Z Fighters plan on using the Namekian Dragon Balls to help them grant certain wishes in chapter #243 of Dragon Ball by Akira Toriyama. Their hope is ostensibly crushed when King Kai informs them that planet Namek likely doesn't have any Dragon Balls because of a massive cataclysm before Kai soon realizes a few Namekians are still alive. To convince the humans that the surviving Namekians won't hurt them, King Kai quickly mentions that Namekians are mostly nice and that King Demon Piccolo likely was as well, but humanity had corrupted him.

Piccolo Turned to EVil Because of Humanity, Just Like Buu

For some, this might have felt like King Kai was giving Demon King Piccolo too much credit. After all, a whole separate Namekian was created from the evil in the Nameless Namekian Warrior's heart, and that Namekian almost single-handedly destroyed Goku by the end of the original Dragon Ball series. However, in chapter #484 of Dragon Ball, Majin Buu transforms into a whole new destructive entity known as Evil Buu after some humans shoot his dog and then Hercule. The narrator in the following chapter describes the transformation as follows: "Boo's anger swelled up within him until it popped out as another body. He was split into the Sweet Boo and the Boo of Pure Wrath."

Of course, Dragon Ball Super would later reveal that Majin Buu was the product of the original Kid Buu devouring the peaceful Grand Supreme Kai, diminishing the evil in Kid Buu's heart. However, Majin Buu was obviously still evil just based on how many humans he easily destroyed even before Super Buu initiated the Human Extinction Attack. Upon bonding with Hercule and their dog, Majin Buu became truly innocent and had even given up destroying the rest of the world. However, when those horrible humans began perpetuating senseless acts of violence against Buu and his "family," the evil actions of those humans caused Buu to create a whole entity that solely consisted of the wrath in Buu's heart.

King Kai's Piccolo Theory Isn't That Different From Evil Buu's Origin

Of course, humanity's evilness also caused Buu to become what the manga termed Sweet Buu or what the anime called Good Buu. This obviously differs from humanity exacerbating the evilness that had created Demon King Piccolo, but not by much. Even though Buu expelled the evilness in his heart and became Good Buu, it still yielded the physical manifestation of evil that would continuously absorb various lifeforms to become Dragon Ball's strongest versions of Buu before finally "devolving" back to his true evil state, Kid Buu. These transformations wouldn't have been possible if those two humans hadn't attacked Majin Buu, Hercule, and their dog. So it's not too much of a stretch to assume that even though Demon King Piccolo was ostensibly made from the evil in the Nameless Namekian Warrior's heart, it was humanity who truly transformed him into the monster that manga readers came to know in the original Dragon Ball just like DBZ's Majin Buu.

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