I'm gonna make this short and straight to the point. I want to end all the threads which ask why Obito and Kakashi are not blind.
The only Mangekyou Sharingan Users who have gone blind are Itachi, Sasuke and Madara. As far as we know they have all had both Amaterasu and Tsukuyomi, and have spammed that indefinitely. The reason why I think they went blind is because they spammed BOTH eyes to use Susanoo which really drains their life force an targets the eye which cannot handle the strain well. Remember when Madara said you need both eyes to awaken their full potential?
The reason Kakashi and Obito are not blind is because they have only ONE MS and don't use both eyes to use one justu that screws up their eyesight by taking a large toll on the user. We have seen Kakashi bleed from the eye because it's worse for him because he's a non-Uchiha. Obito on the other hand is an Uchiha and handles it well. His senju DNA helps him and gives him a better life force and chakra reserve. Since he and Kakashi don't have an MS jutsu like Susanoo which drains his life force and targets his eye, his eyesight is always intact anyways. Hope you enjoyed it and understood.
EDIT: To sum up everything I said, I conclude Susanoo is what does it. Since Sasuke only had it for a week an spammed the hell out of it, he immediately got blind. Amaterasu is the half of the Susanoo that really messes up your eyesight.
The only Mangekyou Sharingan Users who have gone blind are Itachi, Sasuke and Madara. As far as we know they have all had both Amaterasu and Tsukuyomi, and have spammed that indefinitely. The reason why I think they went blind is because they spammed BOTH eyes to use Susanoo which really drains their life force an targets the eye which cannot handle the strain well. Remember when Madara said you need both eyes to awaken their full potential?
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The reason Kakashi and Obito are not blind is because they have only ONE MS and don't use both eyes to use one justu that screws up their eyesight by taking a large toll on the user. We have seen Kakashi bleed from the eye because it's worse for him because he's a non-Uchiha. Obito on the other hand is an Uchiha and handles it well. His senju DNA helps him and gives him a better life force and chakra reserve. Since he and Kakashi don't have an MS jutsu like Susanoo which drains his life force and targets his eye, his eyesight is always intact anyways. Hope you enjoyed it and understood.
EDIT: To sum up everything I said, I conclude Susanoo is what does it. Since Sasuke only had it for a week an spammed the hell out of it, he immediately got blind. Amaterasu is the half of the Susanoo that really messes up your eyesight.
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