Merciful Weapon Fusion
(from Starfinder Core Rulebook)
A weapon with the merciful fusion often hums pleasantly when at rest and makes soft, airy musical noises when it is used to make an attack. The magic of this fusion subdues the damaging effect of the weapon it is added to. While this fusion is active, the weapon’s regular damage becomes nonlethal damage. If the weapon deals two types of damage, both of the damage types become nonlethal. You can activate or deactivate the merciful fusion as a swift action.