Starbright (Starbright #1)

Stella is a Star, sent by a Council of Elders to live on Earth and protect the planet from the Darkness, a terrifying evil that would suck the good from every living thing and leave the planet empty and desolate. She has until her twenty-fifth birthday before the Protectorship becomes hers and Earth is left solely her responsibility. Stella’s fate goes on fast forward as she struggles to balance the rest of high school with the duties of protecting humanity from the deadliest kind of evil. With her parents and Seth, the boy intended to be her Counterpart, by her side she faces down demons and fallen angels in an effort to protect the last inhabited planet in the universe. But evil is not her only enemy. She also fights her future as she tries to decide if she’s willing to give up her human relationships, especially that of her best friend Tristan, in order to save humanity.