This is only a BRIEF, more information to come soon!
Aquarius-Éternus, (formerly known as "Planet Lightwater") is what is known as the Heaven Home to the Waterian race in times of birth, death & re-birth. If a Waterian is lucky enough to remember the world from which they came from, they will be granted full access back there at any time, if needed so after having fallen onto Mobius.
Aquarius-Éternia is half the size of Mobius itself, but it bigger than the moon. The planet is basically made up of ancient underwater sea kingdoms, with themes similar to roman or ancient Greek sculptures & buildings. Some areas stay quite barren & sandy with patches of seaweed & coral, along with many variants of fish roaming the deep, while in equally spaced areas lay each ruling temple or palace structure of each individual Waterian colony. (E.g. Lightwater/Darkwater/Lustwater Kingdom..ect.)
The Lightwater Kingdom being the main capital of the deep sea planet, consisting of a sizable Ancient Ruin-themed city by the name of Aqua-Puris. The Lightwater Kingdom is under rule of a now single standing monarch by the name of Queen Purity, who watches over the Lightwater colony's progression over time, keeping fair rule in check so that no affray will fall upon the underwater land & place of belonging, as it has once been disturbed before.
Twined with the Lightwater Kingdom & it's colony is the Darkwater Kingdom. There have been known to be a total of 3 that have been discovered on Aquarius-Éternus, but there could be more waiting to be found in the future.
It would be very rare for anyone born outside of the planet to gain instant access into it, as there is a special protective layer in the planets atmosphere that stops any random newcomer from entering, this is known as 'The Gate'.
The planet itself had only been known as 'Planet Lightwater' to the members of the I.B.S since they encountered Peach as one of the very first Light-Waterians they had ever met. The now official name for the planet had been considered to 'Aquarius-Éternus' or most often referred as "Aquarius-Éternia" (with thanks to RKizax8 aka Reece (Kiza) Kelly for the idea & suggestion.)
'Aquarius-Éternus' is the Latin meaning for "eternally aquatic" which relates to how the planet has a forever flow of water & has only been made of water ever since the Waterian race existed, as well as relating to how the Waterians that reside there, hope, for their own critical survival that the planet will stay eternally protected with water.