If the anti-magic sword is Licht's, as is mentioned numerous times by now, and taking the witch queen's words about Asta into account, I'm leaning toward the possibility that there's actually more complexity to the plot than first imagined.
Let's see, first, my bad memory is acting to foil my explanation. Didn't Licht receive a 4-leaf griamoire? I'm pretty sure he did. It was sword magic I believe. But Asta's is a 5-leaf clover. so far as I am aware, no one inside the story itself is aware of this fact. It also brings up the question if people in the world are aware of the narrator's statement "5 leaves mean demon," assuming that wasn't the editor's notes, which I don't think is the case here, positively.
Now, here is where things get a bit complicated. Patolli-Licht instantly recognized Asta's griamoire as True-Licht's. But he did so after seeing the swords and what they can do. One sword was in the griamoire. One sword was in the dungeon. Despite the blades triggering recognition everyone's stated, "That griamoire doesn't belong to you/belongs to Licht-sama!"
But Licht's magic doesn't appear to be anti-magic particles from what we see. We don't really get much on his magic during the flashback. Which I believe is very much intentional. All that's displayed is Creaton's Brandish, which appears to be basic cutting. It does cut a tornado, though, so perhaps it was already anti-magic and it simply doesn't explicitly show this for plot-related reasons.
And then we have Nero. The birds are meant to flock to people with less manna. While Nero actually knew or sensed where the second anti-magic sword was located... It also prefers to remain with Asta, similarly to an elemental spirit. My initial impression is that Nero is exactly that, an elemental spirit, but the anti-magic variety. But perhaps he could also be Licht somehow in the spirit of the bird. It's weird to be sure.
Regardless, Nero can tell where the swords are. And he senses lack of magic. this means the swords are devoid of it, atop all other evidence that constantly reaffirms this is how the swords work.
Patolli-Licht's magic is light-sword magic. Asta's is essentially the opposite, black/dirty/rusty sword ant-magic, which a demon clover symbol. There's even a partial transformation.
The obvious conclusion is that True-Licht always possessed anti-magic sword abilities and that his griamoire just worked differently from Asta's somehow to allow for the coexistence of real magic and anti-magic.
That, or something twisted or corrupted Licht's Griamoire into the demon. In which case the monster went on the rampage, was slain by the future magic emperor, and the griamoire was hidden in its crack in the wall all this time until Asta appeared to claim it.
I think Nero may be rather important to all this. He could be just a mascot, but he's already served plot-related functions before, particularly finding Asta the magic-absorption sword. wouldn't surprise me if the bird surrounds how the 4-leaf sword magic became 5-leaf anti-magic. This reveal will likely be the most important of plot points, as it will drive home that Asta's in danger of possessing the power of the legendary demon monster, assuming the two are the same.
