User blog comment:BeoBlade/God Eater Final Punishment Chapter 15/@comment-10225593-20150504121028/@comment-24799642-20150504174703

Didnt explained it very well so here it goes XD

the Doors are basically the open source of the 5 different realitys, Beoblade and Kaitlin (involving all the world of GE) are based on the all new 6th Door, as this Door is new it is the most fragile of the Doors and the only one that can enter different realitys (doors). The "Vessels of the Doors" are the ones who can bring a Door to appear but they need to die or do an exact Trigger event  for it. Each Door contains a different fate, maybe bad or good. Axl wants to destroy all the 5 Doors of the Reality because he knows that if those Doors be destroyed, new 5 Doors will be created and in hope to those Doors to dont have the Aragami existence. Klaus tried to discover the 5 Doors alongside Axl, in hope to save his son (a Vessel) but after what happened in the incidents a little after Klaus Chapter #02, he somewhat changedand became one of it and he was hunting 6th Door members in order to control/ikill they and unlock the 5 Doors.

Vessels for now: Thomas Beoblade, Kaitlin Gristan, Dante, Josua.

Vessels Researchers: Klaus, Nikolas, Axl.