how did Itachi get his mangekyo sharingan

[YIN YANG]

Maybe MS gets activated if you feel responsible for a friends death. The question is how did Shisuis gain the MS

I don't think we know enough to answer that question.

 

[PositiveEmotions]

yea we can all pretty much agree that itachi's ms got activated by shushi's death

 

[YIN YANG]

yea we can all pretty much agree that itachi's ms got activated by shushi's death

yea but if he didn't kill him how was it really activated.

 

[PositiveEmotions]

yea but if he didn't kill him how was it really activated.

maybe the thought of it dude kakashi's ms also got activated dude maybe he finally let go of his feelings of obitos death and his ms got activated and same with itachi i guess

 

[YIN YANG]

maybe the thought of it dude kakashi's ms also got activated dude maybe he finally let go of his feelings of obitos death and his ms got activated and same with itachi i guess

that's possible

 

[PositiveEmotions]

that's possible

so far it seems possible

 

[Floydical]

No, Itachi didn't give Sasuke Tsukiyomi, Amaterasu and Susanoo. He just gave him automatic Amaterasu when he sees Tobi.

Wrong. It says so later in the same chapter the other person referenced that he gave Sasuke all of his abilities:

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Clearly Itachi meant to give Sasuke MS as a result of his battle, but did not plan it the way it happened. Sasuke did already have Itachi's 3 abilities, having them passed to him, but had no way of accessing them w/o MS. Therefore, it seems that Itachi had planned for Sasuke to awaken it after some period of time, after Sasuke started to grieve for his brother in some way. But since Sasuke was told Itachi's truth by Madara, he awakened it immediately, surely something Itachi did not plan on. Basically, Sasuke awakened it from grief, but had all the MS abilities built into him by Itachi before that.

Itachi clearly gained MS from Shisui's death, but exactly how is unclear. It is possible that Shisui controlled him but I'm gonna focus on one fact:

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Itachi is first shown with MS after learning about Shisu's death. So either that was his first time awakening it, and he had no knowledge of Shisui's death up to that point, or he awakened it the night previously when shisui 'died' either by Itachi's hand or simply with Itachi as a witness. Here's one thing to note:

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He said he didn't attend the meeting because he 'was reaching the height' so perhaps he did obtain MS that night.....based on this fact I'd say its possible that Shisui was controlling him with something along the lines of "kill me to obtain your MS". Maybe they both knew about the Uchiha's plan to revolt and made the plan together to isolate himself, show his bad side to Sasuke and set up motive for the massacre....but it's hard to believe it was all under Shisui's control. I like to think that at the very least Itachi accepted the mission at his own will and let Sasuke live as well, but I think that perhaps up to awakening his MS, he was being controlled by shisui.

As for Madara and Izuna, here's the chapter on them:

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The previous page says "they continued to refine their abilities and both of them later obtained MS". This could mean they refined their abilities to the level where they were able to kill their friends (and did) or it simply activated from that training....neither one is clear right now.

And obviously Shisui's methods of obtaining MS are unknown and will never be known IMO, and its not needed in any way. It is assumed he lost someone dear at some point and awakened it, that's all.