I know that this is kind of an old topic, but from what I have seen a lot of members have a misconception about how Sasuke's Enton works and even some even believe that Sasuke preps Amaterasu before on his Susano'o.
Amaterasu
So to start off this is the viz description of Amaterasu from the data book.
The traditional sign of someone using Amaterasu is there eye's bleeding, because of the strain that the technique puts on the user. However there is one occasion of Sasuke using Amaterasu without his eye bleeding.
Some people say that the reason for this is that Sasuke can use small amounts of flames without bleeding, but it most likely an artist mistake because Sasuke in a later chapter uses an even smaller flame and his eyes still bled.
Susano'o
This is Sasuke's susano'o, When in this form with or without legs it has two armaments. A bow, and an orb that resembles flames, but is composed of Susano'o chakra. Sasuke uses this orb to perform shape manipulation and create either swords or an arrow.
When Sasuke was on the brink of exaustion he managed to summon the same level of Susano'o as Itachi and in its right hand was a black flame orb in place of the orb made of Susano'o chakra that he had during v2.
This orb is not Sasuke simply using the technique on the Susano'o hand nor is it Sasuke covering the orb of Susano'o chakra in black. Why???
1. Sasuke's eyes have never bled from summoning the black flame orb, and in case you are one of the ones that believe that is only an issue of the amount of black flames, as I have stated earlier Sasuke has created smaller amaterasu flames in later chapters and his eyes still bled.
2. That orb isn't just covered in Amaterasu flames because it is not as solid.
Enton: Kagutsuchi
Ok, for this section I have a couple of questions. As I have stated there have been no credible instances of Sasuke using amaterasu and his eyes not bleeding so how does this happen?
I actually would like your input on this, but anyway here is my theory on how this works. First lets take a look at Kakashi's Kamui.
This technique is focused on the user's line of sight, just like Amaterasu, but Obito's Kamui works in a different way entirely. From what I can tell Obito's Kamui uses his eye like a whirlpool and sucks either himself or others that his is touching into the Kamui dimension, but there is another function to Obito's Kamui. Obito can channel the technique through his body and place himself in between dimensions and as a result make himself intangible.
I believe that Sasuke's eyes can work in the same way as Obito's Kamui. This is the description for Blaze Release according to the Naruto wikia.
It is possible that Amaterasu and Kagutsuchi in Sasuke's body work in a way to allow Sasuke to produce Blaze Release within Sasuke's body, allowing him to use it in a way similar to his chidori where he can just summon the Enton chakra and utilize the chakra as he sees fit. So if Sasuke can use produce and shape black flames on his own then what use are his eyes? Well, aside from allowing the process to take place Amaterasu fires a greater quantity over at a longer distance. And Kagutsuchi done from the eye can most likely offer greater control and possibly even manipulate Sasuke's flames and from a distance.
Preemptive statement
Some of you might say something like didn't Sasuke just cast Amaterasu on his hand and thin manipulate it with Kagutsuchi this chapter.
If you notice here amaterasu has created an area of melted water that actually overshadows the area that Kaguya left in between Naruto and Sasuke. If the black flames were placed on Sasuke's arm then the water would seep in to area that Kaguya left, but since it didn't Sasuke from the looks of it positioned his flames more to the right of him and Naruto.
Thanks for reading
Amaterasu
So to start off this is the viz description of Amaterasu from the data book.
Amaterasu is the highest level Fire Release technique, that can only be used by those that awaken the Magenkyou Sharingan
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Susano'o
This is Sasuke's susano'o, When in this form with or without legs it has two armaments. A bow, and an orb that resembles flames, but is composed of Susano'o chakra. Sasuke uses this orb to perform shape manipulation and create either swords or an arrow.
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When Sasuke was on the brink of exaustion he managed to summon the same level of Susano'o as Itachi and in its right hand was a black flame orb in place of the orb made of Susano'o chakra that he had during v2.
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This orb is not Sasuke simply using the technique on the Susano'o hand nor is it Sasuke covering the orb of Susano'o chakra in black. Why???
1. Sasuke's eyes have never bled from summoning the black flame orb, and in case you are one of the ones that believe that is only an issue of the amount of black flames, as I have stated earlier Sasuke has created smaller amaterasu flames in later chapters and his eyes still bled.
2. That orb isn't just covered in Amaterasu flames because it is not as solid.
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Enton: Kagutsuchi
Ok, for this section I have a couple of questions. As I have stated there have been no credible instances of Sasuke using amaterasu and his eyes not bleeding so how does this happen?
You must be registered for see images
You must be registered for see images
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I actually would like your input on this, but anyway here is my theory on how this works. First lets take a look at Kakashi's Kamui.
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I believe that Sasuke's eyes can work in the same way as Obito's Kamui. This is the description for Blaze Release according to the Naruto wikia.
And as we know Amaterasu is the technique that produces black flames. Now let us take a look at the description for water releaseBlaze Release (炎遁, Enton; Viz "Inferno Style") is an advanced chakra nature kekkei genkai of the Uchiha clan, that allows them to manipulate black flames.
That is actually the way most elements are. (Outside of manipulating real pre-existing element) The user either user their chakra to create the element or mold their chakra in a way to simulate that element and then manipulate it.Water Release (水遁, Suiton; English TV "Water Style") is one of the basic elemental nature transformation techniques that allow the user to manipulate pre-existing water, or create their own, by turning their chakra into water
It is possible that Amaterasu and Kagutsuchi in Sasuke's body work in a way to allow Sasuke to produce Blaze Release within Sasuke's body, allowing him to use it in a way similar to his chidori where he can just summon the Enton chakra and utilize the chakra as he sees fit. So if Sasuke can use produce and shape black flames on his own then what use are his eyes? Well, aside from allowing the process to take place Amaterasu fires a greater quantity over at a longer distance. And Kagutsuchi done from the eye can most likely offer greater control and possibly even manipulate Sasuke's flames and from a distance.
Preemptive statement
Some of you might say something like didn't Sasuke just cast Amaterasu on his hand and thin manipulate it with Kagutsuchi this chapter.

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If you notice here amaterasu has created an area of melted water that actually overshadows the area that Kaguya left in between Naruto and Sasuke. If the black flames were placed on Sasuke's arm then the water would seep in to area that Kaguya left, but since it didn't Sasuke from the looks of it positioned his flames more to the right of him and Naruto.
Thanks for reading