In his later years, the solitary elderly swordsman Tsuji Gettan has dedicated his entire life to the way of the sword. One day, he comes into possession of a mysterious device capable of traversing space and time. Through this device, he is transported across dimensions and becomes lost in a different world known as the country of Zena.

In this strange new land, Gettans exceptional skill with a blade is recognized by the nations military general. He is tasked with instructing the countrys soldiers in swordsmanship, finding a new sense of purpose in these daily training routines. However, this period of peace is shattered when the hostile nation of Oukoku launches a sudden invasion. Facing this new threat, Gettan sets aside his role as a simple instructor and takes up his sword alongside the soldiers of Zena to fight in a war that is not his own.