Ways to counter that, hmm....
Intense heat, to de-magnetize the metal.
Illusions, to disrupt his sense of balance.
Counter-grapple, using non-conductive arms like treants to grab each circle
Overwhelming offense, since no part of that is going to help him defensively
Faraday Cage might actually be the easiest to pull off.
Almost all solid ideas, though the last two fall a little flat since his own strategy is defense through the sheer offense of his weapon and I don't think a Faraday cage would affect him at all since they simply stop the passage of electromagnetic signals in the air and he's presumably passing them along the wire connecting his chakrams.
The problem with the heat method is that he is utilizing electromagnet energy, and the weapon itself is not a magnet that can lose its charge to control the Chakram's that are attached to each other with a chain.
Unsure if there is illusionary magic in this manga (world) but since he is such a high level I doubt it would work on him as in most manga only low ranking or individuals with a low constitution are affected by debuff's dealing mind effects.
Counter-grapple, using non-conductive arms I think would also be useless unless your agility allowed you to be able to move as fast as lightening since the weapon was moving too fast to be seen when it struck the Demon Centipede adventurers.
As for an overwhelming offense (See above) again he is controlling his weapon with electromagnetic energy that travels as fast as lightening, which would mean that you would have to move faster than 180 million meters per second. Also, since it is a chain weapon it would be similar to trying to approach a person with a razor-edged whip.
The problem with a Faraday Cage is that he is controlling the weapon by holding onto it, thus similiar to a microwave or your car it would not stop his weapon but isolate him with his weapon. The problem is if you ar4e in the faraday cage with him your dead and if you are not in the cage with him then he is free to escape the cage and attack you.
If I utilize the various D&D methods to counter this weapon I would rely on the following:
Utilize the strongest lightning you have to strike the individual and hope he doesn't ground himself.
Utilize Ice to incase the individual and hope that the ice works to stop the flow of electromagnetic energy.
But here again it depends on what skills he has and how he uses them. Currently we only know he has a skill to use electromagnetic energy but does this also allow him the use of lightening. I mean his nick name is Red Thunder.