The Eternal Struggle

This is the name, given in legend, to the mystical conflict between "Love and Chaos" that supposedly underpins the structure of reality.

In reality, it is a reference to the shattered battleground of Earth 0, where Tsukino Usagi and Sailor Chaos Galaxia, in the most primal of continuities, stand deadlocked, forever frozen in an instant of time.

Here, in this time, in this place, the "power of love" never purified Chaos Galaxia, who mortally stabbed Usagi. Usagi, in her last dying moment, desperately wanted this to not be the way things ended, and using all her willpower, rooted both herself and the charging Galaxia in one spot for all time, then sent her life force through the Ginzuishou to create an entirely new reality/multiverse where things went as she most desperately hoped they would, with Galaxia being freed thanks to her outstretched hand of peace.

This underpinning, fueled by prime Usagi's eternal will, keeps all of reality in one piece and ordered against the destructive ravages of Chaos, forming a lynchpin not unlike the function of Yggdrasil in Norse Myth.

Should this prime Usagi's concentration be broken, even for an instant, her hold on reality would break and Galaxia would charge forward, killing her, and dooming the multiverse in an instant.

Today, this primal battleground is considered nothing more than a myth, but it does exist, and has been visited before...

(n.b. This is event 0 and Earth Prime for the SAILORMOON / Subsenshi portion of the Omniverse, not the entire Omniverse itself.)