MAJOR UNMARKED SPOILERS FOLLOW. ABANDON ALL HOPE, YE WHO ENTER HERE
Ninja Ninja represents Afro's repressed thoughts and personality.
This is especially prominent in Resurrection, but in both movies, what he says could be considered Afro's thoughts on the situation—his self doubts, his silly side, all the things Afro isn't. Remember—he first appears at the midnight battle under the Bodhi tree when he gets the Number Two Headband back, after all his closest friends are killed. In Resurrection, nearly all of Ninja Ninja's lines could be considered Afro (or any normal person, for that matter)'s thoughts on the matter—For example:
- In the first movie- "What you just did back there, was it absolutely necessary? I'm beginning to wonder if you have any feeling for human life left in you at all..."
- When Afro first starts his journey anew- "We don't gotta do this, you know... maybe you could pick up a sport or somethin'...'
- At the strip club- "You... uh... do something. I'm gonna go get a lap dance, and meet you in five minutes."
- While eating with Shichigoro- "This is the best in town? Afro, you should kill this guy for lying!"
- Before the fight with Shichigoro- "What's with the formal stance? I mean, he cool and all but he ain't yo' friend. Just dead this fool."
- Upon seeing Afro's father's severed head "This can't be real, man! Who are these people?! This can't be possible!"
And so on. Any of these could be thought of as what Afro's thinking or feeling at the time—He doesn't really like killing, and he's questioning himself, he doesn't want to become the Number Two again, he wants a lap dance, he hates the food, he's questioning why he's using a formal stance rather than just kill Shichigoro normally, and he doesn't want to believe that Sio was holding Afro's father's head.
Another important part- whenever a battle begins, he never sticks around for long- Either he runs off to do other things, or he's incapacitated somehow. In addition, at the end of Afro Samurai, where he "dies", Afro's remark about the two handed grip being twice as powerful as Kuma's Dual-Wielding is thought to be said to Kuma, as though Ninja Ninja was never there. This is because during battles, Afro is focused- he has no time for doubts or jokes, just actions. A point of interest is the one battle he does speak in—the one between Afro and his father. His dialogue consists of telling Afro to kill his father, because it can't possibly really be him, and that Afro's crazy for thinking so. At this point, it becomes obvious that Ninja Ninja is not real, as he is not visible in any point during the battle, and the dialogue between Afro and him takes place in Afro's mind.