When Mōsō was Chief Advisor, he secretly poisoned Ōwashi, which resulted in his death. Sagi, who was really Toki, took on the guise of the Cursed Warrior in hopes of avenging her father.
Many of his techniques are weaker copies of the actual versions (his "summoning technique" activating a projector is just one example, or using strings to make it appear that his enemies have been caught in a Shadow Imitation Technique). His strategy seems to mainly involve deception, which allows him to overcome foes who are stronger than him. Hōki even copied Sasuke Uchiha's Fire Release technique which he used to knock off the Cursed Warrior's mask and even used Water Release techniques in his fight with Naruto. He is, however, talented with genjutsu, as shown in a flashback where he won the trust of the daimyō by appearing to swallow a sword.
When it came to the final conflict, Mōsō trapped her in an imitation technique (discovering Toki's duo identity in the process) at the same moment Naruto, Neji Hyūga, Tenten, and Kakashi Hatake arrived. Mōsō eventually made off with Toki, leaving the Leaf ninja problem to Hokushin and the other Wandering Ninjas. Despite this, Naruto tricked him into revealing his true self when he used water clones to disguise his position. During the attack, Chishima was wounded by Hōki. Naruto defeated him with Naruto Uzumaki Combo. Hōki was handed over to Toki, and Naruto requested that he be forced to repent for what he had done.