I’ll declare it, Mother Flame is called as such because it is the flame that gives Lunarians their special properties. It is the Mother Flame because it is the flame they use to light their own flame for the first time. Like the everburning fire from the Olympics.
All of the Lunarians are children of the Mother Flame. Vegapunk acquired the Mother Flame from King and managed to stoke and keep it artificially.
The World Government is scared of losing it because they don’t know how he did it, maybe they don’t even know of its origins.
Following this rationale, Uranus might’ve been a weapon the Lunarians owned, because we’ve been guessing that the Government has Uranus and I’ve been guessing that the Mother Flames used to run it comes from Lunarians.
It kind of makes sense if you think about it, that weapon was stuck in Mary Geoise until it was sent out to be first used because it acquired its fuel. Mary Geoise is on the Red Line, Lunarians used to be the original aboriginals of the Red Line…
Finally, it makes sense if it think about it thematically. Poseidon is a weapon tied to the sea and its people (the Fishmen), because a mermaid is it. Pluton is a weapon tied to the land and the surface because supposedly humans and/or surface dwellers made it. Uranus would be a weapon tied to the sky people because it is related to a group of sky folk, Lunarians definitely fit the bill being winged and having that “god” culture.
*Theory by Kioga101