Question regarding weapons doing Aggravated damage

I'm sure this has had to come up in someone's campaign...a player is interested in a birthright relic weapon doing aggravated damage.  In my campaign, my players have finally achieved Demigod status and one player wants to get a birthright relic weapon, a firearm in this case, that may do aggravated damage.  I know that characters may do aggravated unarmed damaged with the Crushing Grip/Divine Wrath epic strength knack combo, but am unsure what to do in this case.  Is there something already published within the five books that may cover this?  Maybe charge a Legend point to allow the weapon to do aggravated damage and maybe say the power is worth "X" amount of points per the relic creation rules in the Scion Companion?  "X" being the unknown quantity in this case as I am unsure how powerful this ability would be (I imagine it would exceed at least two relic dots...).  I know the easy way out would be to disallow the relic altogether...but the strength knacks mentioned before seem to almost beg for a ranged equivalent IMHO.

1st, bear in mind there is a Boon to make weapons do aggravated damage, War 5 Mortal Stroke.  Easy rule of thumb, then, is to make it a 5 dot relic.

I have a weapon that does agg in my game, costing 1L per use. I awarded it largely due to the player of the PC with it not investing in Epic Strength much (she has like 2, or maybe 3, and the weapon is basically a tiger claw so not a huge damage bonus).

Sounds interesting, which book is this boon in btw?

Scion Companion, Manifestations of Ichor section.