Core Q&A Expanded Answer
Dagda, First Druid of Erin, gave Druidic Elemental Magic to the Gaels under the Great Agreement between the Gaels and the Tuatha Dé Danann. In Heart of Destiny, he also gives Breanna the knowledge to control all five Elements and to gift any of the Elemental powers to her sworn Warriors of Destiny as she sees fit. Breanna requires her Warriors to earn each Element through merit.