Cast in Fire

Celestia doesn't have a lot of time left and needs someone to inherit her title: Heir of the Sun.

Time is running out. A thousand years have passed and Celestia could feel her strength fading. She would need to choose quickly - choose someone who would inherit her power. And who none better than the one she had looked over for the past couple decades? However, she's very sure that Twilight would not like to hear what the ultimate cost of it is.