[Legal Fish]

Let me tell you, this fight is less about set up and more about tactics.

No, I'm not trying to sound like "ALL JOBS ARE EQUAL!" guy and I'm sure what I just said can be applied to every mission... but I really mean it.

If you prep yourself with stacking Mistmelts on a member(or members) who will be able to use them without hurting your group.

You can go something like

Tank(PLD or NIN) Melee Melee BLM RDM WHM and come out a winner if you play right. Don't be afraid to use Sleep to recover.

I don't remember the strategy exactly, but I've beaten Ouryu with multiple set ups, both normal and manaburn, both with NIN and PLD. It's not impossible and should be a relief after dealing with Mammets.