New Mains!
Squall, lvl 100
SSS, Valiant
Onion Knight, lvl 100
SSS, Tactician
Warrior of Light, lvl 100
SSS, Tactician
Cecil, lvl 100
S, Cautious
Imma share my level trick, just cause I'm so totally sexy like that. xD
The best way to get your rank to SSS, is to fight Exdeath in Quick Battle. He must be lvl 105 for your rank to hit SSS. Most people already know how to set up opponents like this, but in case you don't, it's very simple.
To set up your (COM) opponent to lvl 105, you must set the opponent's Strength to Maximum and his Level to AUTO, it will adjust itself to lvl 105, and he will be SSS rank. The benefit to fighting Exdeath is because his AI is pretty predictable according to most, but for those like me, try Gabranth. They will be pretty tough, but if you have unlocked the Ensanguined Shield, there is a chance they will have it equipped, ensuring a One Hit KO! Although, I like to fight them at their best, but that's just me.
Hope this helps.
P.S. To get SSS rank, it takes A LOT of battles, you may have to fight Exdeath or Gabranth more than 20 times to get from rank D to SSS.