PC: I jump into the air, throw my grenade down and dive. DM: Roll to hit. PC: Nat 20 DM: Opposing guardian shatters to pieces.

Depends how strictly you're sticking to the narrative. -I think guardians dealing with maybe saving or defending groups of the other races from Oryx/savathun taking them. Moral quandary of helping the enemy to stop a very evil army growing. Maybe Variks reaches out in the case of other fallen (we already do so in beyond light) -Going off to do actual jobs for the drifter that might have your guardians questioning their loyalty to either side (there was that one time bungie made us choose between drifter and vanguard but nothing really came of that from a roleplay perspective) -Re exploring raid areas after they've been completed because something's going on. Atheons being rebuilt. Savathun is toying with an Oryx shadow on the dreadnought. -guardians that actually work for Calus, not just on the leviathan (see drifter example above)