A village headman (shoya) from Tosa with the right to carry two swords, Nakaoka was very active in the loyalist movement. A friend and associate of Sakamoto Ryoma, Nakaoaka assisted in efforts to bring Choshu and Satsuma together in their anti-Bakufu alliance. Nakaoka sustained fatal injuries during the assassination of Ryoma, with whom he was staying, at their hideout in the storehouse of the Omiya, a soy seller’s shop in the Kawaramachi district of Kyoto. Although he lingered for two days before succumbing to his wounds, Nakaoka was unable to positively identify his and Ryoma's assassins.
- Hillsborough, Romulus. RYOMA- Life of a Renaissance Samurai. Ridgeback Press, 1999
- Jansen, Marius B. Sakamoto Ryoma and the Meiji Restoration. Columbia University Press, 1994.