The fist to fist fighting style that Isa was using right now was not dealing enough damage. However, she was skeptical if she would be able to do much else with her other elemental energies. The fire could be resisted by the water attribute of the swamp fish man. And so could the ice damage.
However, Grace was proving that some of the attacks were starting to get through. She had just fired a larger ice arrow, almost akin to an ice spear, at the broken scales that Isa had already created.
When Isa spotted that the very end of the large ice arrow had pierced the cracked scales, she was pretty sure that the damages they were doing would eventually wear in to the body of the swamp fish man.
