From Storm in Heaven:

Ten years ago, there was an explosion at Hisano's apartment building. She would have been there, but she'd been hit by a bike ridden by a boy in blood-stained clothes. He dropped a fake gem when it happened, and she's been hanging on to it as a good-luck charm ever since. Now Hisano's in high school. One of her teachers was murdered, and the police are investigating. A young man suddenly appears carrying the toy the gem belonged to. And perhaps... can he also see the hallucinations Hisano has always been plagued with? Everything is connected as the pattern slowly rises to the surface.