1) Create an Esper Affinity. AP builds your affinity with the equiped Espers (Certain characters can only equip certain Espers in this premise. For example Kirin could be equiped by Terra, Celes, Relm, some others perhaps.). As your affinity goes up, two things happen. Firstly, you will learn the spells, which stay on you forever. Secondly, you gain accsess to a certain set of stat boosts that get better as the Affinity goes up. This only applies so long as the esper remains equiped. (Perhaps the same esper could have slightly different stat variebles depending on who has equiped it.)

2) Sabins' Blitz's are physical.

3) Game is made harder.