The Extraterritorial Demon Battlefield was opened in the domain beyond the The Great Primordial World, an unknown distance away, by the Eclosion Sect's supreme leader using supreme divine abilities and the laws of space. It served as a battlefield for tempering Eclosion Sect disciples.
Besides being a testing ground for inner sect disciples, the heavenly demons within were also materials for the Eclosion Sect's pill refinement.
Thus, it was exceedingly important.
After Fang Yu entered the Extraterritorial Demon Battlefield and transformed the Evil-Repelling Divine Lightning into Evil-Repelling Golden Armor, he began searching for the extraterrestrial heavenly demons that other outer sect disciples avoided like the plague and feared immensely.
After all, upon encountering an extraterrestrial heavenly demon, if one's mental will was not firm enough and one fell under its delusion, the lighter consequence would be mental collapse and qi deviation. The heavier consequence would be having one's soul and mind completely devoured by the extraterrestrial heavenly demon, becoming its nourishment and making it even stronger. It might even have a chance to enter the Divine Ability Realm and become a Heavenly Demon King.
However, if a Heavenly Demon King truly appeared, the elders of the Eclosion Heavenly Palace would discover it at once and either take action themselves or send true disciples to kill or capture it.
They would then refine it into pills to consume and enhance their magical power cultivation. This was also what the elders and true disciples of the Eclosion Heavenly Palace were most willing to do.
For a heavenly demon in the Extraterritorial Demon Battlefield to break through and become a Heavenly Demon King, it would have to devour the souls and minds of who knew how many outer sect disciples. From this perspective, outer sect disciples were in fact "leeks" for the Eclosion