User blog comment:ImperiexSeed/The Leviathans Destruction, how's it going to happen?/@comment-3519940-20120308024212/@comment-3481504-20120308033435

Not only that, but Archangels are also stronger, and despite the Leviathans' age, they're smarter; Death may have described them as "cunning", but archangels possess cosmic awareness.

To date, the only things that possess the power to kill them, are Archangels, Jesse Turner, and obviously God and Death.