Sanzokuou manga

Sanzokuou summary:

Nagakado [Seyu] 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 [Seyu] 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 Nagakado's [Seyu's] bloodline. They also passed on a strange star-shaped mark on their chests, and as Nagakado [Seyu] inherits the mark, the mark on his father's chest fades. Soon after Nagakado [Seyu] 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, Nagakado [Seyu] finds that his father has been murdered, hence he sets out for revenge. Along the way, he meets a beautiful assassin named Natsume [ Megumi ] . What adventures could the future hold for these two? Note: The names in the [ ] are the names of the characters from the latest scanlated manga release of this series