Chambers: The Spirit Warrior. Chambers Series

A new warrior, not bound by human form has traveled to this new world and hunts one thing: Cage. Barely escaping China with their lives, Cage and Mia arrive in America early in the nineteenth century. War is raging, as the US military, settlers and native Indians battle the land they seek to call their own. It seems to come alive at times, the phenomena a mystery, but the outcome indisputable: the warrior carries with him a darkness and the ability to attack and control all in his way.
To prevail in this time, Cage draws upon his martial arts training to unlock a source of power so incredible he has to die to attain it. Yet even as Cage races to find answers, subduing his adversaries and outwitting conspirators, Mia is increasingly drawn to use her skills to achieve her personal interests, which include a newfound love. Separated then reunited, the sibling's individual journeys diverge, allowing the evil to fill the void between them.
Intent on reclaiming his sister and preserve innocent lives, Cage must face the dark warrior in a realm where neither of them are fighting in their own bodies. The question will be; if you die when in another form, is it forever?