I've been trying to get this to work ever since I convinced myself that it was possible :-)

https://www.youtube.com/watch?v=rn9Jd2CB5LU

Since the raid boss starts out with 3500 def/spr, I'm taking advantage of fixed damage abilities from Setzer (Double Dice).

For those of you who aren't yet familiar with the mechanics of Double Dice, it has an equal chance to choose 5 possible "rolls" - valued at 11, 111, 5555, 55555 or 77777 damage. This damage doesn't depend on any of Setzer's offensive stats or any of the enemy's defensive stats. It does happen twice with dual wield (and the second hit always uses the same roll as the first hit). It is affected by elemental resistances/weaknesses. It is affected by killer passives. And finally, chain multipliers do apply.

My strategy is to load up one of my Setzers with all the killer passives I can get on him (ultimately 150% damage against both demons and humans), dual wielding, and give him a weapon that I can reduce elemental resistances for. Then I get a friend to do the same and share his Setzer (I think this is possible to do just with my own and a second Setzer with just the elemental weapon, but the odds are pretty rough that way). Then I get them both into a full chain multiplier and pray that I get good rolls on the two good ones.

Ace is around for the -75% Fire/Light/Lightning resistance. Orlandeaus are there to build and sustain a chain multiplier as long as possible, and several chainers could do the same thing effectively enough (atk isn't super-important here, since they end up doing so little damage themselves).