As seen in: The Last Ninja (Commodore 64)
Also in: The Last Ninja 2 (Commodore 64)
Distinguishing feature: Full body ninja costume, revealing only angry eyes and bushy eyebrows.
Strengths: Ninja powers, time traveling.
Weaknesses: Silver. Wait, no, that's werewolves, not ninjas. None, then.
For all of their purported efficiency and ruthlessness, Armakuni and his mystical ninja spirit overlords are a lot that just can't seem to get things done.
Spared from the complete destruction that befell the rest of his compatriots during their big once-per-decade ninja convention, Armakuni had to fight the evil shogun Kunitoki to reclaim the sacred scrolls that gave his order their power. While able to reclaim the scriptures, he was apparently unable to completely finish off Kunitoki, who reappeared hundreds of years later in modern-day New York.
Snatched from his own era, Armakuni was hurled through time by the spirits of his clan to combat Kunitoki once more. Again, Armakuni bested the maniacal shogun and again, somehow let him get away. Which was followed, not surprisingly, by Kunitoki reappearing in a different time and place and Armakuni being sent through time to fight him. Presumably, this would have continued indefinitely -- Armakuni's adventures are a bit of a comedy of errors.
One might wonder why such a powerful ninja as Armakuni cannot seem to ever finish anything he starts. A better question is why, if his magical benefactors can send him through time, do they not just zap Armakuni to some point when Kunitoki is completely helpless? Of course there's no good answer to this, but the fact that The Last Ninja 4 was canceled while being developed (not once but twice) suggests that Armakuni's inability to finish the job is in his blood -- a trait passed straight down from his digital parents.