Nagakado was a fairly normal boy, albeit a trap genius. He and his father lived comfortably in a small town. However, that innocent family had secrets that Nagakado was only half-aware of. Everyone in the family line interited a strange sword, a black katana that is much heavier than it looks and is only usable by people of Nagakado's bloodline. They also passed on a strange star-shaped mark on their chests, and as Nagakado inherits the mark, the mark on his father's chest fades.

Soon after Nagakado learns his family's secrets, his father is accused of treason and is taken away to a larger city. Nagakado follows, carrying along his heavy heirloom. Eventually, Nagakado finds that his father has been murdered and sets out for revenge. Along the way, he meets a beautiful assassin named Natsume. What adventures could the future hold for these two?