So Demonbane's a counter that return opponent's force back to them. Very handy when Ohma was out of breath and had no strength to attack by himself. Fighting Wakatsuki was ideal for this technique, but it would be totally useless against soft technique user like Hatsumi.
The (imaginary) process probably was: flame -- form / body positioning, water -- catch blow, redirection -- redirect the force, adamantine -- hit back. If Ohma could use Fallen Demon like Setsuna, then he could get a perfect timing for it.