First Blue must have the following spells:

Overdrive: Time Magic
Stasis Rune: Rune Magic
Shadow Servant: Shadow Magic

-Go into overdrive.
-Overdrive gives you about five to nine turns depending how experienced you are.
-Cast Shadow Servant.
-Do any spells you want while in overdrive.
-On your last turn in overdrive cast stasis rune.

This will prevent you from losing you JP!
Overdrive will take 10JP each time.
Repeat until you have no JP or the enemy is dead.
If you come out of overdrive without stasis you will lose your JP.
But you will have five to nine turns permanently after stasis rune wears out.

Have fun!