Interesting idea. I'm always a fan of desconstruction of bad fanfic cliches.
AoMythology said:
New Idea: Naruto has the Sharingan; not very original, except it mainly brings him trouble, so it's much more realistic than the usual fare (kind of a deconstruction).
A)He can't get Chakra from the Kyuubi willingly (Kurama would sooner die than have someone with the Sharingan as his container), though he does get the boost in reserves and a slight boost in healing due to the seal used (the canon Eight Trigrams).
Keep in mind that Kurama's chakra apparently only began to enter Naruto's circulatory system around the start of the manga (or shortly after.)
This implies that Naruto's stamina and robust circulatory system (that allows him to mould an amount of chakra that a Jounin would be expected to be capable of) is primarily a result of his Uzumaki heritage. Remember that both Naruto and Kakashi were surprised at Naruto healing faster than normal from his self-inflicted stab wound during the Wave arc.
So any AU fic which has Naruto mastering (or gaining any level of proficiency at using) Kurama's chakra at an absurdly young age like six is entirely unsupported by canon mechanics anyway. I suppose that hypothetically if Danzo or Sarutobi had decided to weaponise Naruto (and actually tailored their teaching style to him,) he could have ended up as an absurd prodigy like Kakashi, but he'd still only start to gain access to Kurama's chakra around the same time that he does in canon. That's just how the 8 Trigrams Seal works.
B )While he is much better at using Yin Release than canon Naruto, he's still not very good for an Uchiha, so he is nowhere near as good at casting genjutsu as Madara or even same-age Sasuke, much less Itachi (and his Chakra Control; well, see point 'L'). He is Ashura's transmigrant still after all. (And no, he doesn't get any other bloodlines, much less the Mokuton* or the Rinnegan.) His Wind Release is still his affinity, but it's still of around average potency, like in canon. He doesn't have Sasuke's supercharged (Lightning) primary affinity, or a Wind equivalent.
Naruto and Sasuke weren't born as Ashura and Indra's transmigrants, and neither were Hashirama and Madara. They ended up attracting their souls and chakra by having similar philosophies (Friendship/Power is the key to peace.) A Naruto with a wildly dissimilar personality to his canon self would never become Ashura's transmigrant.
If Senju/Uzumaki have a genetic predisposition to Yang Release, and Uchiha have a predisposition to Yin, then a Naruto with Uchiha heritage (did Minato have a recessive gene?) would have a natural aptitude for both. That said, if his chakra control still initially sucks, then Genjutsu would't be an option for a long time, and becoming Ashura's transmigrant might temporarily imbalance his chakra and screw up his Genjutsu for a while.
Also, I'm pretty sure that "strong" or "weak" elemental affinities is complete fanon. Canon Naruto doesn't have a "strong wind affinity." He has a wind affinity, meaning he has an easier time learning to create and control wind-natured chakra. It's also only mentioned in the anime that Sasuke has a natural affinity to lightning. Sasuke was taught the Chidori to face Gaara, and probably learned Lightning Transformation over the time-skip to complement it and to enable him to derive other techniques from it, but there's no indication in the manga that Sasuke had an affinity for lightning.
That said, I'd personally keep Naruto's affinity in your fic as wind, as if you didn't, and you plan on having him complete the Rasengan, you'd have to make up a fire version, which people always seem to want to argue about.
E)Dark Naruto is a lot harder to handle than in canon; the only saving grace is that Kurama doesn't back him at all, but he might have a situation similar to Ichigo and his Inner Hollow from early Bleach; after all, an Uchiha full of hatred is stronger than one who's not. (Yes, Naruto's personality is intact from canon; not a NINO, another difference from usual Narutos in such fanfics, or fanfics in general - well, maybe smarter. EVENTUALLY.)
Pretty sure that Dark Naruto would only appear at the Falls of Truth. I was under the impression that it sort of collected all of Naruto's subconscious thoughts, and personified them. A Naruto who's suffering from the Curse of Hatred but who still has his canon personality would obviously have more darker thoughts and impulses "pushed to the back of his mind," but that wouldn't necessarily make the "Dark Naruto" created by the Falls of Truth any stronger. The whole point of the waterfall is that it becomes/creates a mirror, meaning the personified creation is identical in ability. That said, while Dark Sharingan!Naruto wouldn't be any stronger than his counterpart, he'd probably be much harder to overcome, in that Naruto might find it much harder to accept him when Dark Naruto has even more anger and resentment than he did in canon. Naruto might even find himself being overwhelmed, as he was by Kurama's hatred when he first tried to steal his chakra.
F)Tsunade is much more wary of him, and Jiraiya won't let him use the Sharingan much in training. Orochimaru is less likely to try to kill Naruto, at least, and Jiraiya will be able to teach him about Fire Release (not to mention Kakashi's help on countering the Sharingan's weaknesses); on the other hand, Obito is a lot more dangerous and manipulative, despite (due to?) seeing himself in Naruto even more.
...Why? Jiraiya has never been shown to be anti-Uchiha, and if Naruto having the Sharingan makes training easier, then Jiraiya would probably just either train him even harder, or spend even more time "researching."
Besides, the Sharingan's ability to copy Jutsu is kind of overblown. All it does is allow you to memorise hand-seals and let you see how the chakra of a person using a Jutsu moves through their body. Naruto with the Sharingan wouldn't be able to just copy the Rasengan. He'd still need to spend just as much time as he did in canon learning the necessary Shape Manipulation. He wouldn't be able to learn, say, Jiraiya's Earth Release: Swamp of the Underworld without spending a great deal of time and effort to learn Earth Transformation, or whatever techniques use Yang-predominant chakra (Jiraiya's hair-animation jutsu?) without learning that type of "Quality Control."
Kakashi wasn't known as the Copy Nin just because he had a Sharingan. He was known as the Copy Nin because he had a Sharingan and he was a ridiculous genius prodigy who mastered all five basic Nature Transformations, as well as Yin and Yang, as well as becoming proficient enough at Shape Transformation to learn the Rasengan.
I)Subsequently, it will be a lot harder for Sasuke to accept him than the usual Sharingan-Naruto fic, since they aren't friends since early on. They have the canon relationship (one sided rivalry that slowly turns into a full-fledged rivalry, and frienemies), but his possession of the Sharingan may make their relationship either more familial or much, much worse. It's a tossup, really.
While Sasuke's character is hard to read, I'm pretty sure that if he discovered that he had family that wasn't, as far as he at the time knew, a fratricide-committing sociopath, he'd probably be both overjoyed, and terrified that Itachi would come back to finish the job. Which might develop into full-blown hysteria when Itachi tracks down Naruto as he does in canon. I guess maybe he'd also start trying to hammer some basics into Naruto's head.
Actually, I could see Sasuke discovering that he has family driving him even further down Indra's path. I mean, he has
something to lose now. He
has to get stronger. Itachi's after the only family member he has that he doesn't want dead, Konoha just let him waltz right in with his buddy, beat the tar out of some of their strongest Jounin, and then leave without even any pursuit, and were it not for one of the
freaking Legendary Sannin being there, he would have succeeded in obtaining Naruto (and if no-one tells him why Itachi wanted to kidnap Naruto instead of just kill him, Sasuke's imagination might come up with some frightening possibilities.) And what does Kakashi do after all this? Keep talking nonsense about bonds and friendship instead of helping him get stronger so he can kill his brother and protect his cousin.
J)Naruto will find written tests and anything involving Yin Release (like Genjutsu) a lot easier, but he still has the canon trait of needing one-on-one attention from someone who actually cares to shine (and the supercharged physical stamina, so it's like he has ADHD still), so even if he's not the dead last, he's close enough that it won't matter. (If Chouji is dead last and Naruto the second-to-last... well, they'll end up on Ino-Shika-Cho and Team 7 respectively anyway.)
Well, neither Henge nor Bunshin are Genjutsu, so stronger Yin Charka wouldn't be of any benefit from that perspective. That said, it's been theorised on this board that part of the reason Naruto had so much trouble with the Bunshin is that it's a Ninjutsu with a very strong Yin component, being an illusion with no physical aspect, and as such Naruto's copious amounts of physical energy from his Uzumaki heritage hindered him, making him unable to perform the technique until his chakra balanced itself out (which it did by the time he starts learning Senjutsu.)
Of course, even if this is true, and thus a Naruto with the Sharingan would have stamina and chakra that's less imbalanced while at the academy, his
truely awful chakra control would probably mean he'd fail the final exam anyway. Plus, seeing as the Academy is probably primarily theory for Genjutsu (seeing as we never see any Genin use one,) and Naruto would still get "F's" in Cooperation and Classroom Attitude, he'd still be the dead-last.