A blind hitokiri working for Takasugi. He seeks to destroy everything in the world, similar to Takasugi. His level of swordsmanship is such that he can slash an opponent without the latter seeing him unsheathing his sword. However, Nizou's sword was broken by Gintoki during their initial encounter. Nizou later returns and severely injures Katsura and Gintoki using a demonic sword, 'Benizakura' which transmogrifies his arm and fuses the blade with it. The Benizakura acts like a parasite, slowly taking over Okada's body, which causes him to eventually become nothing more than a crazed monster. Due to the sword, his body has undergone several modifications. He later reveals that his entire upper torso has similar cybernetic modifications. He is eventually defeated by Gintoki. Though his fate is unknown, he is assumed deceased due to the effects of the Benizakura.
His name is roughly based on one of the hitokiri of the Bakumatsu era, Okada Izō.