I used to talk here about a theory where Uranus was the name of the Seiryu Dragon from the Uo Uo no mi, and that it comes to life when the fruit is awakened. So far, we haven’t seen Kaido awaken, and we don’t really know if he is already awakened or if he actually can’t do it.
Uranus is the dragon depicted above Ryugu palace in Fishman Island, the dragon in the walls of Alabasta, the dragon in the temple of Onigashima and the dragon that Oda drew when Franky and Nami explained the sea currents in the Grand Line. It was the ruler of the sky, all beast among the earth and sea (sea kings aside), it could manifest thunders, whirlpools, twisters and flames.
In my theory, the Uo Uo no Mi was hidden in God Valley, as it was Uranus, the Rocks Pirates attacked to steal the fruit. Somehow Big Mom stole it and gave it to Kaido, but he couldn’t awaken the fruit.
The World government chased Kaido for years and tried to get the fruit back, but failed. And that’s why Kaido is so strong, and resistent, he ate an ancient weapon. That’s why he created an army of zoans.
From that point there are two possibilities:
– Since Kaido couldn’t awaken Uranus, with time Big Mom and Kaido thought Rocks was wrong about the fruit, and dismissed it has an ancient weapon and just thought it was a powerful zoan fruit. They decided they needed to find the real one.
– Kaido knows theres a way to awaken it, and it’s related to Joyboy, but he’s not sure how exactly. Many years ago, he thought that by becoming Joyboy he’d be able to use it, and that only him could become Joyboy (because he ate Uranus), but he couldn’t, which is why he tells Luffy that he couldn’t be Joyboy either, and also why he said that Luffy was another user who could fully use the potential he had (just like Kaido with Uranus).
Since the World government can’t kill Kaido, they couldn’t recover the weapon, but also knew that he wouldn’t be able to awaken it. So, they decided to get Uranus back using Vegapunk.
During one of the many times the World government managed to capture Kaido, Vegapunk experimented with Kaido’s DNA, and tried to separate the devil fruit from Kaido. Those experiments created the zoan-object hybrids, the Numbers, and the dragons of Punk Hazard.
The final experiment was the fruit Momonosuke ate, which was deemed a “failure” by Vegapunk. Yet, we haven’t been told exactly why. Even though Momonosuke so far has been able to replicate many abilities previously shown or portrayed by Kaido.
So, why it’s a failure? Well, I believe, that Uranus can only be activated by someone with a specific DNA. Kaido thought it had to be Joyboy (because of some prophecy about Joyboy and the ancient weapon or something), but the truth is in the DNA of the Kozuki or Amatsuki clan.
Toki traveled to the future for something, waiting for something Oden told her would happen in 20 years. And she also made sure that one way or another, Momonosuke or Hiyori would be present during the return of Joyboy, why? Because one of them will have to become or use the power of Uranus.
Nor Oden, or Toki could have known that Momo would eat a copy of the Uo Uo no mi, but they knew their children were crucial once Joyboy came to Wano.
So, the copy of the Uo Uo no mi was created so someone could use uranus, but seems it was an exact copy, then it was a failure, because an specific DNA was needed to awaken it. But since Momo is a Kouzoki and also an Amatsuki then, FOR HIM it’s not a failure.
Oden wrote something important in his journal, something that made Momo say that he cannot afford to die. And I think it’s related to the Kouzuki/Amatsuki lineage and their relationship with Uranus.
Kaido wears a sacred garment around his waist because he is an inactive/dormant Uranus.
The Poneglyph that Law found in the basement has a that same sacred garment around it, meaning it’s a very important Poneglyph. I believe, this is Uranus’ Poneglyph.
Food for thought although very unlikely: Somehow the WG or the prior CD managed to control Uranus, and used its power to win the war during the void century. That’s why the fruit was in their possession in God Valley, and it’s also why they became the Celestial Dragons.
Theory by kathuntress (https://www.reddit.com/user/kathuntress)