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Putting all this aside my theory on the fourth is not that he was using time/space ninjutsu, that would be pointless. sure the kunai would allow him to get to places he can't see and avert the risk of time/spacing yourself into the middle of a wall and dieing instantly such as the x-man night shadow or w/e the ******** his name was had been afraid of happening...but more logically...

The seals on the kunai were containing chakra, more specifically the fourth's chakra. Now lets say that the fourth really is the father of naruto...we know 2 things so far...

1) elements of what a person can use with chakra seem to be passed down genetically. All of the uchiha clan which is abunch of interbred hicks basically all use fire jutsu techniques...every...last...one...of...them. If they can't use fire based jutsu? they're considered a pansay and kicked outa the clan until they learn to.

2) If you were paying attention to 1...Naruto uses wind based jutsus apparently even though he fails at techniques and has to abuse leet kyuubiness to learn anything aside from shadow clones.

Back to assuming he fourth is naruto's daddy it would be safe to assume that the fourth also used wind based techniques based on statement number 1. Now if he really was a wind ninjutsu user it would theoretically be possible for the fourth hokage to use a wind jutsu which pulled the air infront of him around his body and behind it creating a small vortex around him which pushed him through the air, or at the very least he could push the air out of infront of him which would make movement far easier and allow you to move much quicker due to the fact of less wind resistance. This opens up the possibility of the fourth using techniques which allow him to 'flicker' around the battlefield moving far faster then any ninja would be able to normally move with physical strength alone but at the same time once you move past your natural limits your body's senses won't be able to keep up with you anymore.

THAT brings us to our next point...the kunai, beings that moving so fast your eyes wouldn't be able to register anything seeing that it would all be a huuuge blur you would need to figure out a way to bypass this...such as kunais with special seals that contain your chakra in them. No longer needing to see you could simply focus only on your chakra, and be able to know your location based on where you know your kunai marked down with your own chakra to be. This would be a technique very similar to the dual fanged tetsuuga of kiba/akamaru's where they spin so fast in the dual headed wolf form they can no longer tell where the hell they're going, but manage to bypass the need of sight by marking them with akamaru's scent and now only need to be able to smell out their foes which they have no problem doing. [/Rant]