I was reading this answer and it got me thinking, how did Sasuke obtain the EMS if Itachi's eyes were in worse condition than his? Itachi's eyes were losing their light, and they weren't in "good" state to be considered a good replacement. How did they heal when they got transplanted?
Firstly, by attaining the Eternal Mangekyō Sharingan through transplantation of eyes (of a blood relative, ideally a sibling's), the following upgrades are received by the user:
- Deteriorating vision is restored.
- Their Mangekyō-based abilities are made stronger and they no longer suffer any negative side-effects from the usage.
- The user will retain all their previous techniques from their original eyes.
- The user will be able to access the Mangekyō abilities of the donor.
So what basically happens is that, the eyes taken from a sibling get a new host and whatever drastic conditions (related to vision) the donor had gone through while they had the eyes, doesn't affect the new host.
In Sasuke's case, his vision was deteriorating, so he decided to transplant his brother's eyes, which were in a similar condition. When the transplantation is completed, he is able to see clearly and moreover, get an increase in his dojutsu skills. This clearly proves that the precious condition of the eyes doesn't reflect to the new owner. There is no other case to prove otherwise.
The person getting the eyes transplanted cannot access the abilities of the donor. This only applies to non-Uchiha, which cannot awaken EMS, thus get the abilities of the original eye owner. This is shown with Danzo (Kotoamatsukami) and Kakashi (Kamui). May 3, 2021 at 12:25
So far only two people have been shown with an EMS, Madara and Sasuke. We don't know what Madara's brother's powers were, but we know about Itachi's. Itachi could use Tsukiyomi and Amaterasu. Sasuke, after gaining the EMS, displayed high proficiency with Amaterasu, and he was able to use Tsukuyomi like techniques on Killer B. May 4, 2021 at 11:09
But Sasuke had Amaterasu in one eye, and Kagatsuchi in the other. That leaves no space for Tsukuyomi, no? May 4, 2021 at 16:48
It's not explicitly stated anywhere that an EMS can't have more than two techniques. So, I guess only Kishimoto can answer this properly? May 6, 2021 at 9:14
Most likely. But nowadays all the solutions to his problems are Hashirama cells, so I doubt this'll be mentioned by him.. May 6, 2021 at 11:40