The Ancient being taking the appearance of a man. The Northerners' ancesters worshipped the elder beings known as Ancients, majestic and large creatures long extinct. Those remaining had temples built around them by the Old people and were seen as gods.
In the reborn world, magic is channeled through them and produced by them.
Geertas, born as the twin, uses this mana to split into two and to manipulate air gaz' into powerful winds.