Since Brian is a Spirit Tamer his first tool for anything is his magic. Spells are based on how many elements he has to summon various Spirits. He gains an element either by finding a Spirit (as a little wisp) or gaining 100% experience from battle he levels up in one of four elements.
To cast a spell press a C button to summon a Spirit of that element. Up is Fire, left is Earth, down is Water, and right is Wind. The first element used determines the element of the spell to be cast. The spell that Brian will cast appears under his HP and MP meter. Other spells Brian can cast by adding more elements appear in the middle of the screen with the spell in the C button direction of the element needed. Spells that are faded cannot be presently cast, and spells in red require more MP. Press A to cast the spell or B to go down one element level. Casting a spell will use MP, and the more elements required the more MP is used.