Ashura

[Rengori]

Casting Wall/Reflect=Win. You're levels are fine, there is no need to level up further. Don't bother getting FuSoYa, as you are unable to use him in the underworld anyway. Ideally, you should have done this BEFORE you lost Kain, but ultimately as long as you have decent healing spells, bolt 2 and blitz you should be able to take out both Ashura and Leviathan no trouble.

There Is no Wall/Reflect in FFIV Advance. The spell names confuse me. And crap, I did NOT know I could go here before losing Kain.
EDIT: Nevermind, I needed to level up Rosa to learn Reflect and beat her quickly.
EDIT 2: Kicked Leviathan's Ass.