User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-109.157.135.195-20111230181038/@comment-184.77.255.73-20111231022053

Demons are spirits (i.e. as ghosts are), not souls. Death specifically stated that Leviathans were created long before "angel and man"; archangels are categorized as angels and are older brothers to the ordinary ones.

Also, we cannot be so quick to label the Leviathans as beasts with no cosmic or magical powers; while it seems quite likely, Great Leviathan (the boss) could be at the level of an archangel or no stronger than a red-eyed demon.