Here's a great way to get some quick souls (400-1,100) in about a minute. Head to the ninth mission, skip past the cutscenes and wait until you're attacked by three angel enemies. Charge Nero's gun and lock onto the leader of the three angels while dodging their attacks. When they swoop and begin to charge up their energy attack, fire your gun locked onto the leader. This will kill all three enemies instantly, netting you an SSS rank, style points, and the aforementioned orbs. You can repeat this process as much as you'd like. What's more, you will occasionally find an unaffected angel after the blast who you can kill for another 100-300 souls.