Sousuke Sagara, Kurz Weber and Melissa Mao get a new mission.  They are all sergeants in a group called Mithril, a private mercenary force.  They are to protect a high school girl named Kaname Chidori in Tokyo.  This girl is what they call a Whispered, she has certain secrets hidden away in her that could be damaging.  Sousuke, who is an awesome warrior, has to attempt to fit into high school for his new assignment and quickly learns that he doesn't quite fit in.