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If Asura was the source of the CoC that Kaido sensed, i guess there's two ways you can think about it:
1st - Asura is Advanced CoC, so if you can use Advanced CoC to coat your limbs or weapons to make them hit things without touching, you could imagine a version of coating your whole body with it and creating new "limbs" of that invisible force field, and those are the 2 shadows and extra 6 swords conjured by Asura, that's why they are a physical manifestation of the user's will, like Kaku said.
2nd - Asura is a different Advanced CoC version, where the user forces his will on the enemy's head to make them believe seeing 2 shadows / 6 extra swords, and because the user is making the target believe that, they get cut by it. The problem with this theory is that Zoro was able to use Asura against a Pacifista, i don't know if they have minds / wills to be manipulated, that's why the first theory makes more sense.
1st - Asura is Advanced CoC, so if you can use Advanced CoC to coat your limbs or weapons to make them hit things without touching, you could imagine a version of coating your whole body with it and creating new "limbs" of that invisible force field, and those are the 2 shadows and extra 6 swords conjured by Asura, that's why they are a physical manifestation of the user's will, like Kaku said.
2nd - Asura is a different Advanced CoC version, where the user forces his will on the enemy's head to make them believe seeing 2 shadows / 6 extra swords, and because the user is making the target believe that, they get cut by it. The problem with this theory is that Zoro was able to use Asura against a Pacifista, i don't know if they have minds / wills to be manipulated, that's why the first theory makes more sense.