I can't find a topic specifically for the shadow plungers, so, did anyone try very hard to figure out who they are? This is the closest thread I could find since they do guard the lesser demon and are essential for the reaches ending.
I've had a couple of theories myself. First I thought they may have been people that were sacrifited to the sword to create it in the first place, they seem to be very similar to the phantom slasher. Or they could be people that died while attacking the lord below. There must be some reason they're guarding the lesser demon, if they're even guarding people from getting to him at all.