Here is a list that shows the amount of spirits you need to acquire certain spells:
7: Power Staff level 1
16: Fire Ball level 3
32: Vampire's Touch
7: Spirit Armor level 1
13: Weakness level 1
16: Rock level 3
34: Rock Shower
7: Healing level 1
10: Soul Searcher level 1
15: Ice Wall
35: Walking Water
6: Restriction level 1
10: Silence level 1
13: Large Cutter
After you have beaten Nepty and have been transported
back to Larapool, make your way back to the ferry that originally brought
you there, get on the ferry and ride it three times. On the third trip,
stay in the cabin and move up to the crates on the right. A "?" will appear
over brian's head, signaling an invisible spirit element!
To get full power without using items, go to a hotel and
say you will stay the night. Then, when at the saving screen, hit B to
escape. You will now have full health.
When an enemy casts a ROCK spell on you, start running directly towards them. You will take control of your character while the boulder is still in the air. If you can get close enough to the enemy, fast enough, the stone will pass harmlessly overhead.