Its good we have some common ground about Sasori not feeling pain.
However, much like all other ninja Sasori has a chakra system provided by his core, it is his means of awakening a inanimate object and making it into his own functioning body.
My argument wasn't that Sasori can't see, can't hear and etc because he doesn't have those organs but rather Genjutsu doesn't work due to the strucutre of his brain.
Genjutsu affects a specific target organ in humans and animals (a section of the brain) which controls temperature and etc, aiming to disrupt that particular section's chakra flow. All i'm saying is, if the target organ doesn't exist as shown with Shino's insects, then Genjutsu doesn't work.
Sasori can see because of chakra networks, same with his hearing, same with his consciousness, he however can't be affected by Genjutsu due to lacking the necessary component in his brain for it to have any effect in disrupting his chakra.
I think you misunderstood what I was saying. You said that Sasori cannot be affected by Genjutsu "due to the lacking the necessary
component in his brain for it to have any effect in disrupting his chakra".
First of all, Sasori doesn't have a brain. You acknowledged this in your original post ("doesn't possess a brain", I think were your words).
Let's say we both accepted that this were true. We both agreed that Sasori doesn't have a brain, so he cannot be affected by Genjutsu. You are arguing this very thing, which is why you are also, if you wish to be consistent, that are arguing that Sasori doesn't need to breath (because he has no respiratory system).
This, however, cannot be the case. And the reason for this is because, if you were to apply the
same logic you used to argue your other points about Sasori's body, but apply it to Sasori's sight or hearing, you would have to conclude that because he has no ears or eyes or brain with an occipital lobe and visual cortext, then Sasori therefore cannot see or hear.
You did not say this directly, but you implied it. Your reasoning must therefore logically be rejected because
this is not the case. Sasori can hear and he can see.
One way or another, you will have to accept the fact that either you fully apply science, and come to the conclusion that Sasori can't see or hear and therefore loses (which cannot be the case)...
or that, in some mystical way (whether by chakra, jutsu, or a simple suspense of belief), Sasori can hear, can see, and can feel (both emotional and physical). If these senses are available to him, then it stands to reason that he can be put under Genjutsu, even if he doesn't have the "component" or "organ" available.
Think about it, he doesn't have any organs and yet he is alive. Laws of the universe are being broken, therefore laws of the universe cannot be applied.
Maybe Sasori can't be affected by Genjustu. But I'll tell you this, it's not because he doesn't have X part of his brain. He doesn't even have a brain. He shouldn't be alive. You're going to have to prove that through some other means--means which I do not believe you can conjure up. Unless you can definitively prove that Sasori is immune to Genjutsu, then we should not throw that under the table when considering what Itachi can use.
Edit: Let me just say though that I have not, by arguing against this, conclude that your entire post is wrong. It is very well thought and organized and I applaud you and commend you for taking the time and effort. I simply disagree with this one component, which is a very important one. Whether or not Itachi can use genjutsu will definitely affect the battle.
It seems somewhat reasonable to say that Sasori is immune to Genjutsu, given the unique state of his existence. However, as I've said before, there is no definitive evidence, at least for me.
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