Sky Note lives in the time beyond the Elements of harmony, beyond the time of the land of Equestria, and beyond the time of Princess Luna. Yes, Luna is dead. This threw off the balance of sun and moon and so Princess Twilight gets a new student.

Night Caster is a good unicorn, she never fought, she didn't hurt anypony. But, everypony hates her. She has a magical problem. She has sudden magical outbursts and magical instability. That's why she's the new student. The new student