Most of the Seraphim and Archangels wield Seraphite weapons against the Demons. As such, the metal is especially effective against the denizens of Hell and beings that use or rely on the sorcery of the Dark.
If an Elemental of darkness or sorcerer wielding shadows as part of their ability is cut by a seraphite blade, the wound burns with holy fire and weakens the user. Rapidly their mastery of shadows will decrease until the wound is healed or the holy fire of the blade forced from their system. Sometimes those affected, especially the most corrupt, fall into a deep fever that the angels call the Heretic's Plague.