Dance in Shadow and Whisper by Sarah Godfrey

Beginning with Kali's point of view and then shifting to the eyes of other characters, the Marionettes of Myth series introduces Pittsburgh as a superhuman metropolis, a world both wild and conquered by the monsters buried in its seams and darkest shadows. The goal of the mission is to protect him, but Kali will find that the only way she can do just that is to break every rule she's been conditioned to follow. Jason's shadow is bigger than he is, and if the leaders of Yuuhi's people find out, Jason won't be human much longer. Yuuhi sees little more than a socially inept emo kid dressed in conflicting shades of black, but Kali only touches Jason's hand, and she feels the sting of something dark and deadly. She and Yuuhi, who was also designated by his own people to be her partner, must find solid proof that Jason is, in fact, a supernatural phenomenon. She can swing a sword with expert precision, but studying popular human teen magazines hasn't taught her how to masquerade as seventeen years old. Ever since the murder of her parents when she was too young to remember, she's been sheltered - and trained. Kali has always been obedient, but when she takes her first step onto a protected 'humans only' high school in suburban Pittsburgh, she knows she was the wrong choice for this mission.

Dance in Shadow and Whisper by Sarah Godfrey