|Fighting Style||Kōgen Ittō-ryū|
|Manga Debut||Act 31|
|Anime Debut||Episode 12|
Nagaoka Mikio is the young heir to the Nagaoka family--a family of prominent former samurai who served under the shogun before the Meiji era. As his family's prosperity fell after the dissolution of the samurai class, Mikio and his wayward friends became a cadre of small-time burglars in order to gain wealth and power.
Setting his sights on the sizable profits earned by the Akabeko restaurant and its owners, the Sekihara family, Mikio conscripts the assistance of Sanjō Tsubame, whose former samurai family served under his before the Meiji era, in stealing from them. Against Tsubame's will, Mikio forces her to infiltrate the Akabeko as a waitress long enough to steal a mold of the key to the Sekihara family's home. Reluctantly, Tsubame does as she is told, but hesitates to hand the mold over to her former master, admonishing that burglary would stain the Nagaoka family's name and honor. Furious at his former vassal's insubordination, Mikio declares that, without a key to the Sekihara house, he and his men will have to resort to murder in the course of their burglary. Their conversation is interrupted by the appearance of Myōjin Yahiko, a young coworker of Tsubame's, and Mikio's men beat the little boy until Tsubame surrenders the key mold.
The next evening, after forging the key, Mikio and his gang descend on the Sekihara house to steal the family's money and belongings, but are interrupted once more by Yahiko, who steals the key from Mikio's pocket and runs off with it, leading the gang away from the house. Yahiko manages to defeat some of Mikio's men with his shinai after corralling them in a narrow alleyway, but the rest flee when they see that Yahiko is being watched over by the infamous brawler Zanza and the mysteriously dangerous rurouni. Oblivious to Yahiko's backup and left alone at the scene, Mikio draws his katana, intending to kill the boy with his family's kenjutsu style Kōgen Ittō-ryū. However, despite an initial advantage, the would-be burglar eventually finds himself outmatched by Yahiko's kenjutsu skills and is soundly defeated.