The reason why demon hunters could fight demons the best way was that they had created a way to being able to use the demonic energy, but in order to not become demons themselves, they don't cultivate it the same way that natural demons do.
Demon hunters practice the normal, classical arts that create qi and elemental energy, but they only use that as a medium to later convert it into the demonic energy.
Right now, Kyle looked at what the man was working on and gasped in surprise. There were at least 25 blueprints of some gate that was enormous in size as well as different options to position it in the city. The gate itself looked like a normal oval door frame but made completely out of some weird material, as well as having a coloured red gem in the top of the frame. The most disturbing thing was that there on the floor where the gate stood, a demonic sign was positioned that Kyle was put into an emotionally unstable state even by looking at it.