In the 15th year of the Kanei Era, a martial arts tournament is held at Edo Castle. In attendance are Shôgun Iemitsu Tokugawa, his sword instructor Munenori Yagyû: Lord of Tajima, and his son Jûbei Yagyû, and from Satsuma, Iehisa Shimazu. At the conclusion of the tournament, Prime Minister Shimazu's 3 fighters, the Nangô brothers, end up victorious. After Munenori deflects a challenge to Jûbei by the 3 men, Jûbei and Iemitsu agree to put on a display of the Yagyû's famous Shinkage-ryû style of swordfighting. During the bout, Jûbei goes mad and repeatedly attacks the Shôgun, his father, the Nangô brothers and the Samurai in attendance, before riding off on horseback. With his son Jûbei now a wanted criminal and his son Matajûrô confined to the Yagyû village, Munenori must make a difficult decision: who will take over for Jûbei and inspect the Nakasen route between Edo and Kyôto. He decides his daughter Akane will disguise herself as a man and call herself Nuinosuke Yagyû. Joining Akane will be longtime Yagyû family friend Tarobei Kaburagi and Ura-Yagyû Arisuke Arisawa. Arisuke's sister Akemi, another member of the Ura-Yagyû ("Secret" Yagyu), will also watch out for Akane and act as chief spy for the group.
Also helping Akane on her journey will be Jûbei, whose madness was all a ruse devised by Tajima and the Shôgun. Working from the shadows, Jûbei disguises himself both as Maboroshi Tengu, a Phantom Goblin who "lurks in the darkness and destroys evil", and as an old man named Gonbei who befriends Okoma and her Yume-no-ya troupe, a groupe of travelling stage performers. Working with Jûbei are the other members of the Ura-Yagyû: Ryûta, Shinsuke, Sôhei, Okiri and Oen, who disguise themselves as accrobats and join the Yume-no-ya troupe. From time to time, wandering half-brother Matahei also assists Akane and Jubei on their mission. As the journey progesses, Akane and her group encounter all sorts of corruption by local town officials and a conspiracy against the Shôgunate by the Satsuma clan led by Iehisa Shimazu. Akane also discovers the truth about her past and is reunited with a long lost relative before finally putting an end to the plot against the Shôgun.