Lady can use Repose (induces Sleep) and White Wind. If you kill Rest before her, she’ll use Arise to bring him back with 9,999 HP. Rest can use a basic attack, his own version of Repose (Death), Doom, Trine (induces Darkness and Silence), Tornado, Meltdown, and Meteor. Meteor only becomes in use after a while… But that’s bad. Because then that’ll be ALL it uses, and may even counter with it (or Trine)!
Begin the fight by first ridding yourself of that annoying b– I mean Lady. Non-elemental is the way to go - Flare and Ultima, notably. In the meantime, start up Golem or Fenrir. Personally, if you want to do some side damage and speed this up some, use Ultima and Meteor too also help hurt Rest.
Rest himself isn’t exactly hard to deal with; just tedious. You’ll need to be healing yourself a bunch, especially later in the fight when he goes into an all-Meteor phase. The best way to simply note when he hits that phase and go all out. He’ll use some of his Reposes upon dying, which Golem or Generir should be able to take over.