The swordsmith Amon accidentally comes across an infant and its dead mother in the forest. Although he is initially overwhelmed by the situation, he finally decides to take the boy with him and thus save him from certain death. Ten years after this fateful encounter, the boy from that time, Gai, is apprenticed to Amon. While making a sword, however, there is a tragic accident in which Gai loses his right arm. Amon then decides to use a sword called Shiryuu to make an artificial arm for Gai. Thus, it begins….