She-Ra and the Princesses of Power. Legend of the Fire Princess

"Even after everything that's happened, the world outside the Horde's walls is still a strange one to Adora. Each day she's learning more about her growing powers as She-Ra, including something new: the ability to heal corrupted runestones. Runestones are the magical source from which princesses like Frosta, Mermista, and Perfuma draw their power, but Glimmer knows of another runestone -- one with a dark past. Long ago a fire princess ruled the lands to the west, until her thirst for power corrupted her, and led to the ruin of her kingdom. Glimmer thinks the lost fire runestone could give the Rebellion an edge in the fight against the Horde, but claiming this ancient power won't be easy ... especially not when the Horde has their eyes set on the same prize."--Provided by publisher