The main character of the story is Shishimaru, the only surviving Iga Ninja from a huge battle between Nobunaga and the Toyatomi. all of his friends are killed in the battle and he wants to fight the samurai to avenge them. He is badly hurt during the fight and rescued by the Koga Ninja. They end up working together to destroy the robot samurai and bring peace to the warring states.
There was a lot of interesting elements present in this story. The fact that they incorporated modern robotics, tanks, guns, and the idea of a space time continuum into ancient Japan is pretty cool. It has a similar feeling to Ninja Scroll in the themes, animation style, and massive violence/blood. The OVA itself runs about 45 minutes. The ending leaves the viewer wondering what is going to become of the world that the main heroes have saved and how all of these elements tie in together.
For the most part, it is well worth the time to watch. If you are in the mood for action filled sword fights paired with some thought proviking themes, then this OVA won't disappoint.