"the 666":
it is a double edged sword that responds to the users emotion, so if they are angry the blade engulfs in fire and if they are racking up some cool combos the blade ices over, when used correctly the user can tell the sword to do what ever he/she wants.
lastly when in demon form, the sword blades extend to double the length and width, the flames/ ice etc... become more potent however the sword becomes lighter and easier to manoeuver enabling the user to pull off better, cooler, more damaging moves easily