Set in the urban Tokyo in the near future, the story revolves around the female protagonist, Touka Kimizuki and her twin brother, Yuuto. Both of them are just like a typical 16-year old high schooler. But they're recruited by Public Security Intelligence Agency (PSIA) to become a secret agent due to their ability to kill skilled assassins while they were still in the middle school. Together with their father who is the Head of Special Activities...