Obito's Mangekyou,the Eternal Mangekyou, and the Rinnegan
There are a lot of complex questions about the many eye techniques of this series and how they all fit together/compare and I am interested to hear peoples thoughts on them and pose some questions of my own.
Lately I have been wondering about Obito's Mangekyou Sharingan and what makes it different from the Eternal Mangekyou and whether it is different from the normal Mangekyou. There are a few oddities about Obito's Mangekyou that I can't really figure out. As we have seen, Obito seems to use his Mangekyou without any apparent consequences to his eyes or health. Every character who has awakened the Eternal Mangekyou suffered severely from its over use. Itachi, Madara, and Sasuke all seem to suffer from blindness and both Itachi and Sasuke showed other physical damage from using the Mangekyou. Obito on the other hand has had his Mangekyou for well over 16 years and he has used it constantly but his eyesight remains completely unchanged and he can use it with no signs of fatigue. The only time we saw any physical limits of his Mangekyou was when Konan pointed out that he can only use it for 5 minutes straight.
We have been told, and shown on multiple occasions, that having Hashirama's DNA strengthens the sharingan. We saw it with Danzou and it was mentioned by Itachi as well. Yet Obito's sharingan seems more than just strengthened, he also doesn't appear to suffer any of the negative side effects of the normal Mangekyou. So far I don't really see any significant differences between the Eternal Mangekyou and the regular Mangekyou besides it having no apparent negative side effects. Even with the Eternal Mangekyou Sasuke hasn't really shown any addition abilities. So is Obito's Sharingan + Hashirama's DNA just as good as the Eternal Mangekyou? Also, if Obito were able to recover his other Eye from Kakashi would he be able to awaken Susanoo or would he have a different power? We have already seen that there are several different Mangekyou abilities but Itachi, Sasuke, and Madara all possess a form of Susanoo. So I am wondering if Susanoo is always the 3rd Mangekyou ability.
So far, the only major difference I can see between the Eternal Mangekyou and the Mangekyou+Hashirama cells, is that the Eternal Mangekyou seems to be a requirement to awaken the Rinnegan. Yet those advantages still seem to be irrelevant for Obito because he already has the Rinnegan.
Another weird thing is that Kakashi really doesn't seem to have suffered much of a loss of eye sight. He has used his Mangekyou quite a bit (especially for a non-Uchiha) and while he claimed to know about the side effects(implying he might have noticed his eyesight failing) that was a long time ago and since then he hasn't really displayed any noticeable impairments besides fatigue.
So what really is the difference between a regular Mangekyou+hashirama DNA and the Eternal Mangekyou? Kishimoto keeps making the eyes in this series more complicated but every time there are more questions that aren't answered.
Another thing I am wondering is, does having only one Rinnegan mean that the user can only use half of the Rinnegan's techniques? As we have seen with the Mangekyou, if the user only has one Mangekyou they can only use one Technique. Each eye has a different ability and having both eyes seems to allow the user to use Susanoo. Obito only has one Rinnegan and so far we have only seen him use a few Rinnegan techniques but is that because he only has one or is it merely because he doesn't choose to use them all. Madara has also only used a few of the Rinnegan's techniques but since he awakened the Rinnegan I always assumed that he could use them all . Nagato was the only one who used all the Path's but it seems like he had to learn them gradually, since he apparently didn't have most of them when he was a student of Jiraiya.
Hopefully we will get more clarification about the eye techniques soon but I am curious to hear theories that people might have on the subject.
Well, in a way, MS + Hashirama Cells (HC) seemingly give you few benefits (if not a few different than EMS, basing on Itachi's comment regarding Shisui's eye, which even as EMS would still probably require the 10 year cool down, which Hashirama cells greatly reduce). It's also possible that while the EMS clears away the blindness effect, the MS+HC might only reduce it (would explain why Kakashi noticed that his eyesight got worse, but not as much as it should for an Uchiha, since it is suggested that the Hatake line comes from Senju, especially those white-haired like Tobirama, this is also suggested for Jiraya, who himself expressed big chakra pool and body capable of using the Sage Mode).
One might actually look at HC as level upper. In a way, MC+HC = EMS, while EMS+HC = Rinnegan, of course it's not quite like that and not that simple, as even Madara didn't gain it over night after implanting the HCs.
In the first place, one have to wonder why the blindness occur. First, one needs to realize that the Eyes are simply a physical manifestation of their powerful spiritual/mind powers. The MS is a level even above that, something to which the body, the physical eyes are not adjusted to. One could even use the term "overclocked". Thus it would be reasonable for the eye to suffer from overuse and the like. The problem with this explanation appears when another overclocked eyes, of closely related person, are implanted. In this case, instead of calling it "overclocking" one should perhaps use the term "poison". Yes, it's possible that the bloodline is truly cursed, or rather, a higher level of seal than the Hyuga's was placed into the blood of the Uchiha. The moment an Uchiha awakens a higher level of power, the MS, a poison is released that constantly eats them way, even if one doesn't use it's power actively (as mentioned a few times), but there is a secret (perhaps in case if that power was needed one day), that poison that comes from the original body, work only on oryginal eyes, while all other eyes have resistance to it. Thus swapping very similar eyes (close blood relation), but still different, allows one to have EMS, immortal EMS with great eyesight. Or perhaps it's more along the lines of fighting poison with even stronger poison and the like. It's never fully explained .
Most Rinnegan abilities use both, eyes and the body, or rather soul and the body. Even when Nagato or his paths, or someone was using powers of the Rinnegan, they were used through their bodies, or the body as the center-source. It's possible that the body might be more important than having both eyes, since it seems more like the power of the soul is properly transfered through proper body or something along those lines. Also, Rinnegan can see other things that seemingly Sharingan and Byakugan can not, like barriers and the like. The fact that each of Pain's bodies could use only one technique of Rinnegan and that each body had to be specifically chosen, does seem to support that explanation.