Sun, Amanda. Paper Gods series.

"After almost a year in Japan, Katie Greene has finally unearthed the terrible secret behind her boyfriend Tomohiro's deadly ability to bring drawings to life--not only is he descended from Kami, the ancient Japanese gods, but he is the heir to a tragedy that occurred long ago, a tragedy that's about to repeat. Even as the blood of a vengeful god rages inside Tomo, Katie is determined to put his dark powers to sleep. In order to do so, she and Tomo must journey to find the three Imperial Treasures of Japan."--Jacket flap