Seed of Darkness by Brandon Rhee

Born a noble of a dying house, Draven fled his home at a young age and struck out as a mercenary. Now, years later, his company takes on a new kind of contract, an assassination. The target of which, casts Draven’s life into turmoil. He embarks on a journey, seeking vengeance against the one responsible, compelled to violence by an inner darkness that augments his strength and speed. He leaves a bloody path of death in his wake with the help of two women, warriors from the Eastern Kingdom known as Thahn. A place where weakness is killed before it has a chance to fester and infect the clans. Torn between his nature as a killer, and the duty to the family he left behind, Draven must ultimately discover what he is, and decide who he will become.