Shisui Uchiha: Full Summary Of The Theory Of Why He's "The One Who Knows Everything"
After the recent revelations in the manga, it's safe to assume that there is solid evidence as to whom "The One Who Knows Everything" is referring to. Through research and simple deduction, it is safe to conclude that the person whom Sasuke wants to speak to is: Shisui Uchiha.
First, Suigetsu finds Sasuke, he tells him that he has found a scroll that has power for them to turn the tide of the war, the most probable power of the scroll is Edo Tensei.
Objection 1: The scroll had the ability to change the tide of the entire war, It's doubtful that it's a simple Edo summoning.
Reply to Objection 1: What Suigetsu exactly said was: "With That, We Hawks Can Rule The Shinobi Worl-..." Suigetsu of course is not the smartest chip in the block, if the Scroll had such tremendous power then why didn't Oro and esp. Kabuto used it before? why keep it stashed in Oro's basement and not use its' power? knowing how power hungry both Oro and Kabuto are, it's out of character for them not to act upon the scroll's power immediately when they can. Suigetsu saw the Edo Tensei army and how powerful they were, in his childish mind he must've thought that with Taka's skills and the power of an edo army they can rule over the world aka it was merely his banal fantasies. And whatever the true nature of the scroll has, one thing is clear: the scroll has the power to facilitate to meet someone, so it's most probably Edo Tensei.
Objection 2: The scroll contains a way to unseal/undo the Reaper Death Seal that would allow Sasuke to meet the Hokages.
Reply to Objection 2a: If we assume that the scroll contains a way to unseal the souls inside the reaper, then the question arises: why didnt orochimaru used it earlier since the soul part of his arms is sealed within the reaper and part of his power within it, surely he would have immediately acted upon it if he had a way to take it back but he didnt.
Reply to Objection 2b: Sasuke wants to know the truth about their clan, The Uchiha Clan and I doubt the Hokages can give intimate details regarding the truth and nature of their clan since the Hokages are outsiders to the clan, they may give their personal views about the Uchihas but they are still outsiders, they did not experience first-hand what the Uchihas felt, and what drove them to do what they did. So it's more probable that Shisui Uchiha can provide Sasuke the answer.
Objection 3: Suigetsu was surprised that Orochimaru would even consider such a task. This man knows Orochimaru very well, hence advised Sasuke not to revive Orochimaru feeling as Sasuke maybe underestimating him. The power of Edo Tensei wouldn't receive such a reaction from Suigetsu
Reply to Objection 3: Suigetsu was merely expressing his reservations in the revival of Oro, knowing Orochimaru's duplicitous and insidious personality that he might try to take power again, and if you remember when Suigetsu said that he said afterwards that "if you just take time you can learn to use it all by yourself" meaning that the scroll has a power that can be learned in due time but Sasuke wanted answers immediately, hence the need to facilitate Oro's revival as an instructor of performing Edo Tensei.
Objection 4: Orochimaru hasn't been able to use any ninjutsu since his encounter with the 3rd Hokage. The scroll could have been saved for other reasons
Reply to Objection 4: Suigetsu already pointed out Oro's arms were sealed, but Sasuke insisted in reviving Oro, possibly to teach him how to do the prepatations and hand signs needed to perform Edo Tensei himself.
Objection 5 : After reading the scroll, Sasuke himself stated how this was something only Orochimaru can do. Knowing Others have performed Edo Tensei already, it is therefore impossible for the scroll to contain the power of Edo Tensei because Edo Tensei can be performed by anyone given the right prep and knowldge.
Reply to Objection 5: Sasuke said that, and yet Suigetsu countered that by stating that if Sasuke took time to study it he can learn to use the power of the scroll himself, therefore the power of the scroll is not limited to Orochimaru only, by taking time anyone can learn it, and Sasuke doesn't have much time, nor was he known as a very patient guy, he wants answers and he wants them quickly. Also like I stated in my original post, Orochimaru could know specifically where Shisui's body is hidden or kept guarded by the Foundation, hence, Sasuke needs Oro also to pinpoint the exact location of where Shisui's corpse is hidden/interred.
Objection 6: Sasuke already watched Kabuto release Edo, also Itachi already briefly discussed the basis of Edo infront of Sasuke. At this point, needing Orochimaru other than the whereabouts of someone would only make sense.
Reply to Objection 6: Releasing an Edo and Summoning them are completely different, naturally Sasuke doesn't want to "unsummon" anyone but wants to summon someone in order to speak to. Also, If the scroll contains the location of someone, then why did Suigetsu asks "who is this one who knows everything person?" after Sasuke looked at the scroll and said he'll meet this certain person, and Suigetsu said further afterwards that in time Sasuke could learn how to use the power of the scroll, if you take the contextual meaning of that, it means prior to that statement Suigetsu already surmised that Sasuke needed Orochimaru's expertise on how to use that scroll, given that Oro's hands are sealed, his knowledge of the preparations and proper usage of Edo Tensei would greatly expediate Sasuke's learning time on how to use it himself.
Objection 7: It would appear that the scroll gave Sasuke the idea to revive Orochimaru and to use Edo Tensei on Shisui Uchiha, regardless of having prior knowledge about this, which is implausible.
Reply to Objection 7: , Sasuke had no initial intentions to seek this "The One Who Knows Everything" only after Itachi gave him his memories did he suddenly have the resolve to talk to this person, you can see by Sasuke's reaction from reading the scroll that its' powers facilitates a meeting/encounter with the person he was just thinking about. Sasuke didn't order Suigetsu or Jugo to retrieve it they found it themselves, and as luck would have it, the scroll has the power to give Sasuke the opportunity to meet this someone to finally put his lingering questions to rest.
Objection 8: Orochimaru explicitly asked Sasuke "why do you want to meet them?" in the plural, meaning it's more than one person,.
Reply to Objection 8: Orochimaru was the only one to refer to "The One Who Knows Everything" in the plural sense, both Sasuke and Suigetsu explicitly referred to them in the singular. Chapter 592 P. 13 Sasuke: This is it... The One.. Who Knows... Everything" Chapter 592 P.14 Sasuke: "I'm goint to meet the one who knows everything"; Chapter 593 P.1 Suigetsu: "Who is this person who knows everything?" there are two possible answers: 1. It was a mistranslation from Japanese to English of the singular noun to the plural form or 2. It is possible that it is not only Shisui who Sasuke plans to talk to but the former being the primary candidate to answer the major questions troubling Sasuke.
Moving on: Sasuke said "I want to know about Itachi's feelings, the feelings of a person who, even after getting his name sullied and dying, continue to think about his village and wanted to protect it"
Objection 9: It is possible that there are other persons besides Shisui who knew Itachi's feelings, he interacted with the other Konoha ninjas, the ANBU, the Akatsuki, there are many people who can relate to Itachi's feelings.
Reply to Objection 9: There is only one person who endured the same thing that Itachi did, one who, despite his name being marred, and himself dying, continue to care about Konoha and wants to protect it. It is Shisui:
"Shisui was perplexed that the clan would not deter from the coup d'etat that they were planning and about the consequences that would follow their actions. He told Itachi that he had tried to use Kotoamatsukami to stop them, but Danzō Shimura stole his right eye, adamant on protecting the village his own way. Fearing that Danzō would get the other one as well, Shisui entrusted the other to Itachi telling him to protect the village and the Uchiha name. In order to prevent conflict from arising over his eyes within the clan"
Objection 10: Shisui's name was not damaged/sullied like Itachi's
Reply to Objection 10: Sullied in the sense that Shisui was probably vilified, Shisui wanted to go the middle way and didn't support the planned Uchiha coup nor did he want Konoha to do drastic actions against his clan, so either of the two factions he didn't fully support or probably both earned him animosity much like Itachi's
Hence Sasuke's Question: What is Itachi's feelings is best answered by his best friend: Shisui Uchiha
The next question of Sasuke is: "What is our clan?"
Objection 11: The Hokages are better fit to answer Sasuke's question: "What is a/our clan?
Reply to Objection 11: Sasuke wants to know the truth about their clan, The Uchiha Clan and I doubt the Hokages can give intimate details regarding the truth and nature of their clan since the Hokages are outsiders to the clan, they may give their personal views about the Uchihas but they are still outsiders, they did not experience first-hand what the Uchihas felt, and what drove them to do what they did. So it's more probable that Shisui Uchiha can provide Sasuke the answer.Sasuke asking the Hokages the truth and nature of their clan is like asking your neighbor about the truth and nature of your family, you're neighbor can only give opinions, not inside information and not first-hand accounts. Further, it is clearly shown in the recent chapter (616) that they were going to a specific place within the vicinity of Konoha, the reaper is not located in any specific place for it is summoned by using RDS and not by searching for it in a specified location.
Hence Sasuke's question: Whati s our clan? is best answered by Shisui Uchiha, Sasuke would likely listen to an Uchiha over anyone else at this point, especially one who has the same ideals as Naruto, but was Itachi's close friend.
The next question of Sasuke is: "What is a village?"
Objection 12: Izuna and the Sons of the Sage are the best candidates to answer this question for Sasuke:
Reply to Objection 12: The sons of the Sages and Izuna died before the founding of Konoha or any village for that matter, so they will be unable to answer this question, also, the sons of the Sage existed before konoha was founded, why would they be located/ lived in a place founded centuries after they died? and also adding doubt that they were the ones they are seeking is the fact that since they were powerful individuals, why didn't Oro resurrect them long ago and used them to conquer the world?
Thoughts on ch. 616 onwards:
My prime suspicion is that it is Shisui Uchiha's body that they are seeking and Oro will use the scroll to Edo Tensei him, since Shisui's body was missing, I suspect Danzo took his body for safe keeping or for experimentation purposes but did not want Oro to acquire it, Oro and Danzo were in connivance before so Oro probably knew where Shisui's body was but Danzo kept it safe guarded from him. Sasuke having acquired Itachi's memory of the events must have also been made aware of Shisui's corpse hidden by Danzo, Itachi probably knew or suspected Danzo's hand in the disappearance of Shisui's corpse but didn't try to recover it because of his secret pact with Konoha to kill his clan and work as an undercover spy within Akatsuki, for if he tried to steal the body he would have acted in betrayal against the leaf and Danzo who was a leader of it. That would've also jeopardized Sasuke's safety when he was still living in the village.
Other point of interest:
(Excerpt from the Sasuke Novel, ch.1 Thunder Chronicles - The Day when the Wolf Howle)
"Sasuke is dreaming. He's standing in a dark forest. There's a red moon in the sky. Weird beasts try to attack him. He throws a kunai at them and they disperse into dozens of ravens. Then, a young masked boy appears. The boy and Sasuke exchange words. The boy questions Tobi's motives. "Why didn't Tobi tell you about Itachi earlier? If he had, you wouldn't have had to kill him. It's clear Tobi wanted to make your hatred grow." It seems the boy wants Sasuke not to trust Tobi. Sasuke asks if this is a dream. The boy neither denies nor affirms this. He says they're at the bottom of Sasuke's consciousness. The boy's last words are: "Remember: I am you, I am Itachi, I am the single witness who saw the rise and fall of the Uchiha Clan." The boy disperses in countless ravens and the dream ends."[/I]
You can see he is clearly not Itachi in the dream, he says to Sasuke :
"Why didn't Tobi tell you about Itachi earlier? If he had, you wouldn't have had to kill him. It's clear Tobi wanted to make your hatred grow."
Then he goes on and says:
Remember: I am you, I am Itachi
He is not claiming to be Itachi himself, but that he is like Itachi (in mindset and beliefs) and he is also like Sasuke (being both of the Uchiha clan) only Shisui fits the characteristics of this person in the dream. It is true that he is most probably dead but the departed have ways to communicate with the living through otherworldly means.