Black flames covered Arthur from head to toe and his strength was greatly boosted. He decided to rely on long-range attacks since Makaze is absent and replacing it with a sword made from Dark Magic isn't that effective.
More than a hundred spears and blades from Dark Magic materialized behind Arthur and with his signal, they flew at the target, who jumped from one place to another, easily avoiding them.
They just weren't fast enough to hit the transformed Claudia, who's already in her strongest dragonic form. Just as she was to dodge the last spear, thin chains sprung from the ground and wrapped around her left feet hence slowing her movements and immobilizing her for a split second.
The time bought by those chains allowed the dark spear to clash with Claudia's crossed arms and despite resisting and dispersing the Dark Spear, direct contact with it was all what Arthur needed.