The Egg of the Perfect World is an apostle, but he also bares a brand (on his tongue).
How can an apostle be branded?
My guess is that since his sacrifice was the world which he aims to replace with a new one that will hatch from within him, due to the fact that must die in this process he became branded himself, as he also had to sacrifice himself for this purpose... but I'm not sure. Does anyone have any more insight?
I'm fine with spoilers -- I'm up-to-date with the manga.
Also, is he the only branded apostle?