Harmony of Bullets

Combat

When wielding multiple sonic weapons, you can modulate their frequencies to allow them to musically amplify each other when operated together.

Multi-Weapon Fighting.

When you make a full attack with two or more small arms that deal sonic damage or with two or more operative melee weapons that deal sonic damage, increase the damage dealt by one of those weapons by an amount equal to your Charisma modifier. In addition, if two or more of those attacks hit the same target, combine the damage from those attacks before applying the target’s sonic energy resistance or hardness, if any.