If it clarifies anything, the elements like fire or water that come out of the sword when using a breathing technique are not real. It's just that the swordsman wields his katana to imitate that "element" in a specific scenario, like a water current. As for anyone who is watching, the movement resembles so much a water current that you can actually see one. So, even Gyu "barrier", as you guys named, is made out of his sword wielding, it's not an actual barrier.