Charlie doesn't believe in destiny, unfortunately destiny believes in him.
Accosted by a small clay, feline figurine, Charlie finds himself the chosen of the Cat Spirit, one of the Seven Great Spirits who protect the Balance of Existence. When he wakes up with a tail that will not go away no matter how he ignores it, he has to believe what is going on is real.
At eighteen, Charlie isn't old, but he's two years past the threshold for dealing with magic for the first time, apparently. This makes him weird, even in Between, a realm of magic, prophecy and shapeshifting. He could live without the earthquakes, thanks.
So now he has to: figure out magic; get along with five scarily competent sixteen year olds and one prickly vampire to form a team; and last but not least, be prepared to go to any world, in any universe when sent there by the Seer, so the Balance of Existence isn't destroyed by agents of chaos. All of which his mentor, Akari, assures him he did say yes to, even if he doesn't remember that part!
Charlie has never thought of himself as a hero, but Existence depends on him coming to terms with the fact that he is.