When that girl makes you fight the red and blue spirits they give you a lot of exp points

First go in to the room where Carman was kidnapped. There should be 4 round things around the machine. Talk to it and u will teleport to another room. There will be people in machines to save in every single room. You only have to save Carmen Roi Len and the guy with the blue hair with Corney as his Guardian Ghost. The Final Boss will power down from lvl99 to lvl 22

Spirit of Fire can only be gotten through the following method.
You must maximum have 19 spirits to get Spirit of Fire.
Push these buttons at the title screen.
Right, Right, L, Left+R, Down, R, Right, B. Once you hear a sound, just press start and visit your spirit list. Spirit of Fire will be only level 1.