Lost Odyssey

When the battle starts, you will have to fist kill Obsidian Miasma, then Fu will summon 2 Reverse Souls. To kill the Reverse Souls, you must cast Death on them. When they are down, turn your forces on Fu.

Don't forget to be constantly healing your party and cast support spells. By this stage of the game, you should be well accustomed in how to battle.

These videos belong to SplitPlaythru (aka Split Infinity). All credit to him.

See his written walkthrough on a complete strategy on how to defeat Fu plus all other bosses. Also includes all items and guarantees Treasure Trove. I can vouch for it, I used it and got 1000gs from it.

Walkthrough at GameFAQs: http://www.gamefaqs.com/console/xbox360/file/928334/51920

For this battle your party should be level 60+, it should consist of Kaim or Seth, who ever is strongest, Jansen, Ming and Sara and of course Mack who is compulsory in the battle. Make sure Ming and Sara know lvl 8 Black magic and lvl 3 composite magic. Also make sure you have Durandai and Durandai ring for kaim, or if you choose seth for your front row get her sword and ring instead.

Fu isn't the problem in this battle it's the Reverse souls he summons after the Obsidian Miasma is down. They will use the 'Sacrifice self' spell to resurrect any reverse soul you've killed and it will completely heal any damage you've done on Fu.

Have Mack constantly cast Gamble on Fu, and have Jansen cast windus on Fu. They should be killed in 1-3 turns, don't bother healing them because they will almost certainly die straight after. Instead consantrait on your 3 immortals. Try and keep the Reverse souls at the same HP because if one goes down then the other will use 'Sacrifice Self' the turn after. Have Sara cast 'All Windus' every turn shes alive, have Ming use Double Cast and cast Flarus on both of the Reverse Souls, and have Kaim keep attacking Fu. If you Have the Durandai ring equiped then Fu shouldn't take 2 many hits.