S-ranking Ledah, I can't do it! Options

[Angelic Chao§]

How do you do it? I know you have to use ice, raise fire resistance, but i don't have anything to raise fire resistance. I will go to any length to S-Rank him, and I have the best weapon that basicly auto kills him but it only gives me an A What do i do?

[Dr Strum]

The best weapon that auto kills him?
Are you referring to Fanelia or Longinus? Because you need to finish with a LVL3 or EXL overskill to get the S (LVL2 is possible, but hard, and LVL1 and 0 I believe are possible with cheating...).
You don't need to raise your fire resistance at all, that will just make you take less damage.
Bring Lina and either Cierra or Serene (Serene for the strong against Fire, or Cierra for the not weak against Fire and high MGC). You could bring Fia if you would prefer her over Serene and Cierra.
Lina should be used to deal damage while raising the OD gauge, Ein pretty much the same, while the other character (most likely a very slow one unless you chose Fia), should be using high-damage over skills. Don't let Ledah transform though, meaning do not let him get a turn under 1500 HP.