Anti Magic 「
This form of magic allows the user to nullify other forms of magic. In order to use it to its full potential, specific spells are required, which are stored within grimoires. With Anti Magic Weapons, the user can utilize different types of Anti Magic but requires someone without any magic power. This is such because of Anti Magic naturally opposing any mana and magic it encounters, and thus, not even the Sorcery Emperor can wield it without having their magic being sapped.
It appears to be a form of magic that has died out in Asta's generation and the previous one before it. No one seems to recognize it and they often show surprise when Asta first uses it. Even the Sorcery Emperor, Julius Novochronos, shows alarm when he held the Demon-Slayer Sword and felt it sapping away his mana. The only people who recognized the swords were Licht and his comrades and the Queen of Witches, all who seem to have lived for many generations.
The only known person other than Asta who wielded the Demon-Slayer Sword and the Demon-Dweller Sword was the elder of the Elf Tribe. It is unknown how he was able to use Anti Magic since the elves were a powerful, "mana-loved" group of beings with mana on par with the Queen of Witches.