One in Ice was a theory that Adam told Crystal. Those who mastered the elements would soon reach a point where they could become one with the element and not be harmed by it.
But such a state was only possible for those who reached the peak of Brayvion. Some had to train in it, others sought fortunes and powers that would help their bodies resist it, and some were merely born in it.
The power of the Ice Soul Maiden could easily enter into this trance state. The frost would be like an extended body to them. And since Ice Heart Maidens were born from Ice Soul Maidens' influence, the power to control and link their ice was believed to be easy. But as for Cryshela, she was the daughter born from the frozen mattress of her mother's womb, which formed the Ice Soul Maiden. Her power could even be said to be of Crystal!
Crystal could not move if she concentrated on keeping up the One in Ice state, so she planned to use Cryshela as the 'pilot' of the giant ice golem.