First, although firearms are strong, the Void Things have a variety of tactics like Virtualizing Spirit Body, Flying Escape, tearing through space, Death Replacement, Clones... An endless stream of incomprehensible methods, and they're not idiots either—they sense danger and will do everything possible to stay alive.
Second, the explosive power of firearms is too great; the instant high temperature and destructive force, even if it hits the Void Things, will turn them into nothing. Then how can we collect the necessary materials for scientific research and manufacturing, and improve the quality of the Void Blade?
Currently in the Void Realm, we can use firearms, even nuclear weapons, with reckless abandon, but if the Void Things run into crowded areas, in our world, we would still mostly need to deploy Martial Arts experts to prevent extensive secondary damage from firearms.
