Naruto's Kekkei Genkai
This theory fills in major holes involving Yondy, Naruto, and the kyuubi. To be specific, how the FTG works, how Minato split the kyuubi's chakra then seal only the yang half in baby Naruto as well as make a key to tighten the seal, why Naruto shouldn't use "that" jutsu, and why Minato chose to seal the kyuubi in his newborn son.
My japanese horrible but I have pick up on the name meanings. Well, we all know that rasengan means spiraling sphere, with rasen- meaning spiral and -gan meaning sphere. But -gan also means eye. So rasengan could be a doujutsu as well as a technique.
We all know that there are three great doujutsu in Naruto, with each one corresponding to a type of jutsu.
But what about Fuuinjutsu? Shouldn't there be a technique for that too? In my opinion there is. The Rasengan (from here on, (R)asengan is the doujutsu, (r)asengan is the technique) seems to fit the bill.
Where's the proof? When Sandaime sealed Orochimaru's arms, he was struggling the whole time. So how did Yondaime manage to split AND seal the powerful kyuubi in Naruto? Well if the Rasengan were able to see chakra flow, nature flow, and the chakra network, then Yondaime would've been able to find the quickest way to split the kyuubi's chakra then seal the yang portion in Naruto so that the kyuubi's chakra flow into Naruto could be controlled with a "key". Now Yondaime probably summoned the key toad and made the key before he sealed the kyuubi. If that were the case, then the Rasengan probably made Fuuinjutsu as easy as doodles to the user, to the point where Yondaime could plan out the key seal in advance and keep Naruto a safe distance away during the sealing process.
Now Yondaime probably knew that if he possessed the Rasengan, then Naruto was very likely to as well. And if Naruto awakened the Rasengan, he might be able to control the seal without needing the key to do so. Maybe that's why Jiraiya asked the key toad to seal himself in Naruto if he died or whatever. He might have thought that the pain of his death might awaken Naruto's Rasengan. But we have yet to see.
"That" jutsu is a very touchy subject. But if Jiraiya did teach Naruto a jutsu that he shouldn't use, maybe Naruto needs to fufill a requirement first, like awakening the Rasengan. This jutsu is probably a Fuuinjutsu that can control the kyuubi's seal. But to do so requires severe chakra control otherwise the seal might loosen too much, releasing the kyuubi. Jiraiya probably found this out when he was training Nauto over 2-1/2 years. But naruto lacked chakra control resulting in the seal loosening a little too much, causing Naruto's frequent tail growth. Jiraiya probably told Naruto about the Rasengan so in the event that he awakened it, he could control "that" jutsu.
I also mentioned that the Rasengan would be able to see the chakra and nature flow, as well as the chakra network. If Minato infused his FTG shiki(?) with the right amount of chakra/nature, the shiki would light up like a beacon to someone with the Rasengan. This helps you confirm that you marked your target, as well as give you the correct destination when using the FTG. If that were the case, this might explain why noone (except possibly Tobi) has copied or learned it. If it could be copied, Kakashi would be constantly using it!
Plus if the Rasengan doesn't exist, then Naruto's up a creek without a paddle, because Pein has the Rin'negan, and Tobi and Sasuke have Sharingan, possibly even MS. The only way Naruto would stand a chance is if he awakened his father's lost doujutsu.
So what do you think? Good or bad? Or really bad (please say no!)?