Half a year has passed since Sousuke Sagara took up the job of protecting Kaname Chidori and has started living like a normal teenager for the first time. A former child soldier, his view on the perils of everyday life is highly unconventional and in frequent need of violent adjustment; Kaname can only hope her endless assault will eventually get him used to normal life. But a shadow looms over their happy days as Sousuke's employer, the private army called Mithril, is attacked by a new unknown enemy. Suddenly outgunned, can Mithril afford to keep one of their best playing around?