There was once a time in history when wars were happening all over Japan during the Fuedal Era... Samurai went into battle time and time again only to kill for corrupt warlords who were to cowardly to face the battlefield themselves.
There was once a great warrior named Jin Tokikaze, he was of the Oshura bloodline and could harness dark chi.
He was very dangerous and many nations wanted him on there side, the dark chi isnt a gift it's a curse. The curse to control and he became a wandering samurai, mercilessly slaughtering any foes who would face him no matter the cause he didnt show mercy.
Later he gave up being a samurai and it was a abnormal occurence but the dark chi curse had different intentions. It knew that if the host (Jin Tokikaze) had a child the curse would live on...