The invader didn't just need raw power to get into the world, but to also adapt to it. After all, even if it could brute force his way into the world, the world would also not just wait idly.
In dire straits, a world could conjure a power that was beyond what any immortal could comprehend. It could call down storms that would blast apart an immortal, or even spew the flames of its core, burning down everything.
But this was only when its baseline laws were violated. The Invader overcame them all by becoming a part of a being that was originally a resident of the world. Now, even if the world wanted to expel the invader by any means, it couldn't.
As it would mean harming one of its residents, which it could not do. This was a natural law that it was born with and simply could not be violated at all.
~CRACK~
~CRACK~
