User blog comment:ImperiexSeed/ARCHANGEL or LEVIATHAN!/@comment-25146716-20141211173713/@comment-24834479-20141212004955

Leviathan can kill angels, and archangels are a type of Angel. Unless it is stated otherwise in the show, leviathan can kill archangel. Even if an archangel can apport all the ingredients and kill the Leviathan, that still doesn't change the fact that leviathan are a weakness for archangels.