The twelve cosmic continents of the Legendary Plains were extremely special and magical, and there was a reason they were called 'cosmic continents.'
The first reason a Cosmic Continent can birth life planets and life galaxies, also known as elemental planets and elemental galaxies, is that they are a unique and rare phenomenon of Legendary Plains.
These elemental planets and elemental galaxies exist within the chaotic space of the Zodiac Plains. Chaotic Space is a special place where only law-tier entities can enter, and anyone else will be torn into shreds.
Anyhow, when an elemental planet or elemental galaxy appeared, it caused a special phenomenon in the area known as the Cosmic Providence, and a Cosmic Gateway was formed that led to an elemental planet or elemental galaxy filled with rare resources, sometimes even ancient artifacts and unknown treasures.
