What if some planets had "no gun zones". These could be places with certain atmospheric properties that render guns useless. This means that all species would be forced to use melee weapons, or just simply bash with their gun(which would be less effective than using a sword). I'm imagining a fortress built on a floating rock, the substance that makes up the rock would have the effect of an EMP. With your guns being completely unusable, your group will need to work together to find some effective melee weapons. A few weaker classed Fallen are patrolling up ahead. One of your mates runs forward to distract them, while you and the rest of your team beats them to death from behind. You take the swords from their limp bodies and continue onward.