Five years after promising his friend Kojiro Kanemaki that they'd become samurai together, Musashi works as a miner while secretly training, in a world where demons are now worshipped instead of feared and samurai have fallen into disgrace. When Kojiro, who abandoned the samurai path, saves Musashi's life, the two fifteen-year-olds set out on horseback to reclaim the samurai's honor and take down the demons preying on the countryside.