User blog comment:ImperiexSeed/The oldest being, archangel or leviathan?/@comment-3481504-20120608025050/@comment-3481504-20120608221528

Haha, you're funny. Tehehe

The Devil alone could take the Leviathan race.

Also, as seemingly Cas, while wielding all of Purgatory's souls accessed the Leviathans' indestructibility, it would seem he had access to all their powers, so if what you says is true, he wouldn't have worried about Michael and Lucifer, as under your perspective, they're unaffected by Archangels powers, too.

However, I will say this, Leviathan can eat EVERYTHING (however NOT God or Death, of course) from Eve to Angels, but not Archangels.