Onimusha: Way of the Sword offers a New Game Plus mode, giving players a way to boost the challenge after finishing the game once, most notably for those chasing a full Platinum trophy completion. The mode is unlocked after completing the main story and starts players on Carnage Mode, the game's hardest difficulty setting, offering a fresh test for those who mastered the standard run.

New Game Plus carries over certain elements from the completed save, though story-locked features such as Haori Pouch switching still won't be available until reached again naturally. Side content progress, Clothing, Weapon and Gauntlet levels, and any stockpiled Red Souls are all reset, so players are advised to spend their Red Souls before starting a new playthrough. Difficulty can only be chosen at the outset, with switching allowed between Action and Story modes at Spirit Mirrors, except on Carnage Mode, which cannot be downgraded once selected; players wanting extra challenge on a first run are advised to avoid items or turn off enemy health bars, while enabling Action Prompts can help those struggling with tougher fights.