Nagato 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 Nagato was only half-aware of. Everyone in the family line inherited a strange sword, a black katana that is much heavier than it looks and is only usable by people of Nagato's bloodline. They also passed on a strange star-shaped mark on their chests, and as Nagato inherits the mark, the mark on his father's chest fades.

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