Momonosuke when he ate the Uo Uo no Mi, Model: Seiryu became Uranus, and he is needed to bring forth the new Dawn, just like Shirahoshi:
The Ancient Weapon Poseidon is needed to change the world – in other words – bring about the new Dawn.
4) Awakening: Kozuki Toki
The final puzzle piece, that brings this all together is none other than Toki. She is the key to all of this.
She is the only living person canonically to have come from the void century, we don’t know her origin, her motives, or why she was going to Wano.
So I would assume she was trying to go to Wano to revive the Ancient Weapon Uranus through Momonosuke. She might have a unique lineage factor that is needed to trigger the Awakening of Uranus (which she passed to Momonuske I mean when she had him). It seems to be the only viable answer to why the fruit is considered a legend and why it has not awakened for centuries.
For the Gorosei, Toki, the only living remnant of a century no one knows nothing off, has literally been off the face of the planet for centuries, assumed dead. That is why the fruit, or Uranus, was incapable of being awakened, even if the devil fruit exists and had users before Momonosuke. Kaido was not able to awaken Uranus (its Ancient Weapon powers) because he isn’t of Toki’s (and possibly the Kozuki Clan) lineage.
Momonosuke with Uranus, like Shirahoshi, and probably like Pluton, are needed to bring about the new Dawn. They are Ancient Weapons.
*Theory by SnooSongs4297