From Fallen Syndicate:

Since the death of his family in a mysterious fire, Nanasawa Io has lived as an outcast. Students at his school fear him and animals around him soon begin popping up dead. This brings about an investigation into Io by a group know as the Titans. The Titans goal is to hunt down and destroy Kagetsuki- people who have become possessed by malicious shadows. However, what the Titans soon discover about Io isn't what they expected.