Raina had no idea of who she was or where she came from, but the four seraphs that captured/rescued her said she was the vesseland they were there to supply the seed.
When all of the elements came together they would produce a force powerful enough to save the world. She was the lightthe giver of lifethe flame of creation. They were Earth, Wind, Fire and Water.
She was pretty sure they were nutsbeautiful but looney.
On the other hand, it transpired that they could do some pretty amazing shit .