1. Naruto's three-time testing
I write this down to the inconsistencies that do crop up in any given shounen manga, due to the way the industry tends to work. Basically, an author can only have their work remain in Shounen Jump and the like if they continue to receive enough fan mail. So, the typical mangaka will keep the script from being fully plotted ahead so that they have plenty of leeway to change things to the fans' liking.
I don't like that system at all, but it explains just about everything.
Anyway...
The way I see it, the Academy graduation tests are likely done at regular intervals, on a voluntary basis - one must sign up to take the test. This helps keep things structured, and makes it easier to have possible Jounin-sensei on standby to take teams.
There would also be a limited number of slots available for testing, in multiples of three, so that there wouldn't be any passing students who had no team, or teams that go short by one genin. (If Tsunade has her way, that might become four students to a team.)
That's as good a paradigm as I can conceive at the moment. So, in this situation, Naruto signs himself onto the test-takers' list as soon as he's applicable, not paying attention to his own ability to pass the test at all. He fails every time until Mizuki's plot.
Iruka likely tried to discourage Naruto from doing this, but Naruto has demonstrated time and again the ability to tone out Iruka's lectures. Since the decision rests with the student, not the teacher, Iruka didn't have a say in whether Naruto could take the test or not. So, Iruka resigned himself to judging the test as fairly and without bias as he was able.
2. Elemental Chakra
Yes, I think it does fit. Kakashi was surprised way back in the bell test at Sasuke's ability to use Goukakyuu no Jutsu, and commented that nobody lower than chuunin should have been able to use it; thus it does have some backing that elemental control is considered a chuunin-level skill. Furthermore, nothing was stated that contradicts the concept, and it does fit well enough with the tone of the series.
My personal opinion on the matter is not so positive. I mean, jeez, it's so cliche!
3. Sharingan: Cheating Made Easy
(yes, I know.
)
Here's the way I puzzle out the ranks of the Sharingan, and their requirements and limitations. For my mind, I imagine that each level builds on the previous one.
One comma bestows sharpened visual reflexes, meaning fast-moving objects become easier to track. Also, it gives the user the ability to see the presence of chakra in the user's FOV - somewhat like the Byakugan, although Sharingan doesn't give the x-ray 360-degree long-distance vision. This likely would allow the user to detect low-level genjutsu by the presence of chakra in the environment.
The requirement for this is likely mere practice and visual exercise, as normal people can accomplish something similar. The difference is in the use of chakra in the eyes, to enable the Sharingan to see normal chakra in the visible spectrum and to enhance the tracking ability beyond what should be possible.
The second comma is when the copying aspect comes in. Furthering the chakra-vision and fast tracking of the first comma, it adds temporary neural connections to the processing and memory centers of the brain. When a ninjutsu or taijutsu technique is witnessed by 2C Sharingan, a part of the brain automatically records the chakra usage and body movements, thus the user copies the skill.
Another effect of gaining this stage is the ability to detect the difference between bunshin and real bodies, and to see through stronger genjutsu. The skill-copy abilities can detail the subtle nuances of chakra flow, thus Kage Bunshin and the like would show up as "not the same" compared to normal bodies.
The requirement for gaining the second comma is obviously being forced to do so through a life-or-death situation. Obito and Sasuke both got theirs this way. It's also apparent that a certain amount of chakra control experience is necessary.
The third comma introduces the movement prediction ability. Since Kakashi stated that the Sharingan can't see the future, I conclude that 3C Sharingan acts somewhat like a chess computer. Its chakra-vision and speed-tracking abilities have become so advanced that the analysis part of the brain set aside for the Sharingan can use the target's body posture, chakra flow, and other data to determine the most likely action the target will take, and then relay that conclusion to the user's consciousness. This manifests itself in a "pre-image" of the opponent's attack showing up in the user's field of view.
The requirement for this is uncertain to me (and would likely be a closely kept Uchiha secret). However, I suspect it to be (not counting lots of practice with the second stage) the state of mental turmoil that comes from willingly acting against one's own strong convictions.
Mangekyou Sharingan is a form that I don't think of as being another level, but rather an "overdrive gear" of the third level. I decided this because A. it's the only form that doesn't always activate whenever the Sharingan is used, B. it doesn't seem to bestow any skills that build off of the earlier levels, instead giving the user access to entirely new doujutsu, and C. it damages the user's eyes.
The two abilities clearly named in the manga are Tsukiyomi and Amaterasu. Tsukiyomi is the "three days of hell in an instant" killer genjutsu technique, which is especially dangerous in that the only thing the user has to do to trap a target in it is to make eye contact. Amaterasu somehow produces black flames that cannot be extinguished by normal means; Jiraiya himself had to seal the flames in a highest-rank seal jutsu to stop them. (The fan-speculated "Susanoo" Mangekyou art is just that: speculation. There is no evidence to even suggest the existence of such a technique.)
The requirements for this form are stated to be "killing your closest friend" by Itachi. This fits my idea of the third level's requirement, and takes it one step further: instead of merely going against one's principles, in killing their closest friend, one is acting against that which they hold most dear. This would undeniably cause an astonishing degree of mental turmoil in the would-be Mangekyou user, which pushes the third-level Sharingan into "overdrive".
On Kakashi's Sharingan
Kakashi's body is suitable for hosting the Sharingan, but since he's no Uchiha, it's not naturally wired for it. So, it uses chakra inefficiently and tires him out faster.
The ability to evolve the level-2 eye to third level strikes me as odd, but not irreconcilable to logic, since Itachi only commented on Kakashi's inability to use Mangekyou.
I don't think Kakashi's "Mangekyou Sharingan" is actually the real deal. I think it's an incomplete version, since the "blades" on it aren't fully filled-in. My guess is that he attempted to unlock it by drawing on his memories of the comrades he lost, coupled with deep hypnosis. However, since he knows that he is not the guilty party in their deaths, his mind can't slip into the insanity that Mangekyou thrives on. (ninja-edit) Since Kakashi's not-quite-Mangekyou Sharingan is an aberration, and he likely doesn't have any knowledge of the real MS arts (which the Uchiha kept hidden in their main house), he seems to have made a new technique for his incomplete version. This one is obviously not an easy technique to do, since it drains a large amount of chakra (which Kakashi admits to not having all that much of) and distorts the user's vision, making it hard to aim.
That's the whole of my theory. Now as for my personal opinion on it, I don't think Kishimoto made the Sharingan too powerful - I think he made
Sasuke too powerful. The Sharingan is a damn dirty cheat, but they're
ninja! The whole point of ninja battle is to cheat better than the opposition!
4. Medic-nin and their art
This one is tricky, as its ups and downs haven't been fully explored in the manga.
Basically, it's stated that the user must have perfect chakra control, wasting no chakra in either the molding or in the jutsu. Also, they must have a surgeon's precision and mental focus. If any of those is lacking, the jutsu could harm instead of healing.
As for the requirements of doing the medic-nin's job successfully, I'd include two more: stamina and patience. Rush a healing job, and something will go wrong; any good doctor would say the same. A high level of endurance is required for those jobs like Neji's patch-job after his fight with Kidoumaru, where a high-level medical jutsu had to be maintained for hours before it was finished.
It seems that in cases where living tissue must be replaced, a medical jutsu can do the job as long as two materials are provided: an ample amount of organic material, and a DNA sample to give it a blueprint on which to work.
Regarding medic-nin fighting... well, I think it's pretty stupid, to be honest. You could have a ninja who knows a fair amount of medical jutsu, but didn't go as far as the ER surgeons - in effect, a shinobi field surgeon - and that'd be fine, but that ninja would still have to be kept off the front line. Exposing your medic to the brunt of the battle means endangering the lives of those wounded who the medic might otherwise have been able to save.
On the assumption that it's necessary, a medic-nin's battle skills should be focused on abilities that either get the nin out of the thick of things, or knock the enemy back far enough to allow the medic-nin to do their job.
Again, the manga didn't go in-depth enough on the subject for deep speculation.
5. Curse Seal
It seems to work on a twisted version of the Eight Gates. It draws out chakra automatically, but also wears down the body of the user (for those familiar with DBZ, it seems to be an evil bastardization of the Kaioh-ken). What each different type of seal - e.g., Sasuke and Anko's seals are the "heaven seal", while Kimimaro's was the "Gaia seal" - does, what differentiates them, is unknown.
The intended side effect of accepting and using the curse seal is that, each time it's used, the user is twisted further and further into becoming Orochimaru's puppet. Judging by Sasuke's dark downturn after accepting the seal, it does its job well.
Curse seal level 2 requires the user to undergo a near-death experience. When they use it, they fully immerse their bodies in the corruption of the seal. This causes their bodies to be transformed to a shape unique to the user, as well as amplifying the effects of the normal cursed seal.
One of the stated side-effects of the cursed seal is that it ultimately limits the potential of the user. It never said that the user would never grow beyond their current level, merely that they would not be able to reach the same level they would be able to on their own. Still, it's very annoying to have Sasuke made out as some insurmountable foe that even the Nine-tailed Demon Fox fears.
Personally, I think that the Curse Seal is appropriate for someone like Orochimaru to use. I would have thought Sasuke would fight it and be determined to go it alone as always, but he's apparently too much of a pussy to kill his brother without Orochimaru there to hold his hand.
