Magic
It is believed that throughout history only those individuals with an extreme sense of their surroundings (meaning nature) are able to connect to them on a spiritual level and express this connection by affecting (modifying) said surroundings on a whim. For many centuries humans were able to use (and misuse) this fantastic ability and even built an empire based solely of, by, and for individuals with the ability to use Magic. The Kingdom of Zeal, as this empire was better known, fanatically pursued the illusion to control and even expand Mana through far-reaching study from their best erudites until the time of their destruction with the Mamon Machine. It was after this catastrophe that the surviving humans tried to amend for the sins of the people of The Kingdom of Zeal by working together side by side to survive the last vestiges of the Ice Age while loosing any knowledege of the use of Magic until it became a myth; or worse, a synonym of the Mystics. But forgetting about it does not mean vanishing it, for the talent only lays dormant yearning to come alive once more.
Personality
Depending on the personality, or more explicitly, on the ability to cope with the responsability inherited by the magical ability of the practitioner, they may further develop said ability and even expand onto other types of magic.
Types of Magic
There are three main types of Magic in Chrono Trigger: Lightning, Fire, and Water/Ice; and these in turn combine to create the fourth type: Shadow. Although extremely powerful separately (Single Techs), it is through combinations of any two (Double Techs), or even three of them (Triple Techs) that more resilient enemies can be defeated.