<p>We truely don't know how the Rinnegen's immunity worked against the Infinite Tsukuoyomi. Sasuke looked so confident in using his Susanoo to protect against the Infinite Tsukuyomi. It's as if he knew it would work, like someone told him it. So it could be either that he did it all in a quick guess or Maybe the Sage said that he could use it like that, if Madara is succesful in IT. It could also be that Susanoo is knowm to. work like that against powerful genjutsu, who knows what.
</p><p>But going with how Sasuke's Susanoo is made of his own Six Paths Chakra, it could be that he just might be immune to IT without Susanoo, or it could not.
</p><p>Though why Ketsuryagan worked against Sasuke is what I believe, he didn't use his Rinnegen. He covered his Rinnegen behind his hair, supposedly stopping it from acting. It's like how Kakashi isn't exactly immune to Genjutsu as much as he is with while he's using his Sharingan while he covers it.
</p><p>It's like that, I believe.
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