You guys have any ideas for something I can do to spice this Item of Power up a bit?
Are you looking for mechanical differentiation or background/story?
If it's the latter, I recommend giving the weapon three things:
- A beginning or pivot point. What turned the sword into a demon hunter?
- An internal conflict. What causes the sword to fail or perhaps even change goals?
- A purpose. (You've done this already.)
An example might be something like this:
The Black Saber of Meriri is crudely forged from a fireplace poker which was used to pin the demon Meriri to the ground while priests completed a banishment ritual. Afterwards, the poker had taken on some of the power generated by both demon and spell and was given to House Chantraine to protect. At some point, a Chantraine scion forged it into a blade.
Wielders since then have occasionally mentioned a feeling of intense hunger when taking up the blade. A few complain of hearing inarticulate mutterings and wonder if the demon Meriri is somehow bound to the blade. One wielder is known to have used the blade to take his own life.
For the last few generations, the blade has been held by the Clan and used by their hunters when normal weapons proved insufficient.