Japan, 2241. As a result of the "3rd Crisis of Man", the surface of the Earth has become uninhabitable for human beings. Among the ruins, only robots remain.

But one of them (a Yojimbot, a samurai robot) unexpectedly stumbles upon Hiro, a young boy, and his father who are trying to escape from an armed troop. The Yojimbot breaks away from the squad and saves the child. He will soon understand that the fate of humanity depends on Hiro's survival.