As far as we currently know, the combat in Final Fantasy XV is going to be your basic action RPG format with single button presses for attacks. So how is the magic going to work then? While he wouldn't offer specifics, director Hajime Tabata did reveal some interesting aspects of the combat mechanics in his game.
When entering combat in Final Fantasy XV, players will execute attacks by pressing an attack button, director Tabata confirmed in an interview with Weekly Famitsu. By keeping the attack button pressed, or by repeatedly pressing the button, your character will execute a preset combo. This looks to be the very basic framework of combat and very likely the bare-bones sort of play we've seen in almost every trailer or gameplay video so far.