Oath of desecration can be casted by someone else on the rogue, but you don't need it.
With Fast Track you get Haste and Walk in Shadows you get invisibility.
You will be delaying your turns a lot/passing (Other characters won't have as much initiative or speed), but it will be worthwhile. Sometimes opponents that can't see you end their turns right beside you which leads to their inevitable deaths.
The most important thing is, you don't want to be in the middle of battle, but in the borders, otherwise all enemies may be looking at you making it impossible to sneak to get your damage boost.
So a good pair would be a rogue and a shield-bearing warrior. Or buffed madora to attract attention.
