How could someone with Magic wield the Anti-magic weapons? The Witch Queen told Asta and his friends a bit about the history of the elves in Black Clover Episode 65. She stated that the elves possessed great magical abilities and were so strong that many of them were her equal in terms of magical strength (and she is very prideful; for her to admit that says a lot.)

What is really baffling me thou is when she stated that the leader of the elves was the former wielder of the Anti-Magic weapons that Asta currently uses, which subsequently blew Asta's mind and mine too!



How is it possible if people with Magic can't wield them? 
We know that the only reason that Asta can use those swords is because he was born without magic and hence the sword does not weaken him. However, the leader of the elves possessed strong magical powers and yet he could still wield the Anti magic weapons. Even the Wizard King admitted that only people without Magic could wield those weapons. Are there any exceptional rules to how the Anti magic weapons work?
From recent manga all of this has been answered.

Three swords already have the ability we see today with the exception of anti magic. That is the Demon slayer sword already had the ability to cut and deflect magic when Licht was the owner of this grimoire. (This is why Licht was able to cut the storm in which Tetia the princess was stuck.) Similarly the Demon dweller sword already had the power to absorb surrounding people and the owner magic spells and release it as flying slash and to glow after it has absorbed certain amount of magic and the Demon destroyer sword other than able to cut magic and spells. It also already had the ability to absorb and remove the effect of spells. 

So anyone with magic would have been able to wield them. This is why they were present in a four leaf grimoire because of its tremendous strength and also before this grimoire became five leaf grimoire these swords were shiny. It is after the grimoire became a five leaf grimoire and housed a demon that they became dark and shady and were able to absorb anti magic from the grimoire in which the demon resides.