I just thought of something neat. It's not a new weapon, but an enchantment.

X% chance for a free turn after a kill.

The idea is to attach it to a weapon, and if you get a kill with it, there's a percentage chance (capped at 33% at most) that if you get a kill, you immediately get another turn, all your action points restored, that sort of thing. It would probably be best placed on weaker weapons like daggers and such so it doesn't get too overpowering, and it should only apply to kills with the weapon, not magic or anything else.

I got the idea from watching an LP of the old Strategy RPG Jeanne D'arc, where that was one of Jeanne's gimmicks in transformed form.