There is a world with a different history: In 1945, mysterious “Phantom Beasts” came from nowhere and attack them. From that time, mankind has been fighting and fighting. It’s been over 50 years! Facing this unprecedented danger, humankind, for the first time, has united in fighting against their elusive enemy.

Now it is 1999. Most of the world is conquered and people barely survive. However, they still fight against the Phantom Beasts using weapons such as the “Humanoid walking Tank(HWT). The last forefront in Japan is the Kyushu area where people are preparing to intercept the beast. Unfortunately a great number of soldiers in their 20’s and 30’s are lost in the battles. Now, boys and girls of high-school-age are sent to the battlefield. Our hero, Atsushi Hayami and the members of Unit 5121 are thrust into battle. Nobody knows when the war will end but they keep fighting in hope for the future. They fight proudly with HWT…”Spirit of Samurai”!