Yukio is a liability in this fight. The chip in his head means he could be taken over by her at any time and could turn his weapons against the other members of the Carnival. But this is the big fight at the end of the story, like something out of a battle manga, and there's no way Yukio would just stand back and watch it happen.

She may be thirty feet tall and covered in metal and smoke, but Yukio is a sniper with a magical energy knockout rifle, so he uses it, getting into position and firing off a shot at her head.

It probably won't work, but it's worth a try.