Near the end of the movie, it is revealed that Ichirouhiko is actually a human boy just like Kyuuta. Iozen found him in the human world and decided to keep him.
After Kumatetsu beats Iozen in the battle for the throne, Ichirouhiko's darkness in his heart consumes him and he stabs Kumatetsu and then disappears.
Later on, he goes out of control and causes a bunch of havoc in the human world, but eventually goes back to normal after Kyuuta defeats him.
