>a small island nation based off of feudal Japan (Sengoku period)
>two clans duking it out to control this island; one of these clans are losing so badly that they learn a corrupting sword art in order to turn the tide of war.
>this winning clan is now ruled by a cult trying to bring about a terrible oni lord who wears the skins of his defeated foes.
>also, the Heavenly Kings that ruled this land are either dead or dying