How about something as simple as a weaponskill?

Phantom Blade: Absorb (reset) your party's emnity and deliver a five-fold attack. Attack power varies with party emnity.

You're lowering everyone else's emnity, you're gaining that emnity and you're dealing damage based on that. It's perfect for when you have a heavy DD party.

You keep emnity down and your party just needs to "recharge" their emnity in order to get the best effect of this ability.