Nine SHs (Beside Luffy) can be grouped based on their Origin,
Isolated Trio = Those who were asked to Join from their Home Island, where They lived Isolated from others (Usopp, Chopper, Jinbe)
Lost Trio = Those whose Homes are still out there, but They cannot go back for different reasons (Zoro, Sanji, Franky)
Homeless Trio = Those whose Homes were Destroyed (Nami, Robin & Brook)
Oda used this with Moon People among many other examples,
As Skypieans lived in Skypiea, Shandians were forced out of their Homes, while Birkans Home was Destroyed by Enel.
I want you to always pay attention to this pattern of Isolated + Lost + Homeless throughout entire Story.
Now for Ancient Weapons, I discovered after much deeper analysis of this Pattern that last one (To be recruited) of each Trio represents a Mini-Version of what those Weapons are. In other words, Ancient Weapons are based on Jinbe, Franky & Brook.
Jinbe have Unique Ability of communicating & summoning/controlling Whale Sharks, no other Fishman have such Ability,
Poseidon is basically World Ending Version of this. I also don't need to explain how Pluton is basically a World Ending Version of Battle Frankies.
This leaves us with Brook, and Uranus gonna be a World Ending Version of Brook's Unique Ability.
It's not being Alive, it's not being a talking Skeleton, it's not Soul Manipulation, it's not Hypnosis or his Swordsmanship/Music, Brook's Unique Ability is the Fact that He has only DF that is able to enter Afterlife, every single DF leaves it's User once They die, meaning No DF can access Afterlife, except Brook's!
And such Journey, allowed his Soul to connect to Afterlife & for example summon it's Chill,
Uranus is basically Brook's Ability but on Steroids, a Weapon that connects to Real Heaven/Hell, allowing you to bring out World Ending Calamities from there, it's like imagine having the power to turn entire World into an Impel Down Level or a Skypiea Trial, that's what it can potentially do.
And all Ancient Weapons together complete each other,
It's no different than what most Villains we've seen before want, They wanted to turn a Place into their HQ (Uranus can do that), They wanted to have an Army & Great Military Power (Poseidon can do that), They wanted to nuke whatever/whoever stands in their way (Pluton can do that).
Based on all of this, imo Uranus cannot be a Weapon hidden in a Box (Possibility is still there though ofc), it's probably a Person or a Soul or Unique Being similar to Brook.