As long as Strength is at 255, Agility is 220+, you have Celestial Weapons and Auto-Haste, Nemesis is easy. Use Quick Hit until Nemesis has a turn, and summon an aeon to take the hit. Then go back to Quick Hits. Just summon an aeon whenever Nemesis has a turn and you'll not have to heal once. Just don't use an Overdrive, as he counters them.