So we all know that gai can fight sharingan users by not looking at their eyes so that takes away genjutsu used through the sharingan. But what about normal genjutsu, like the one used on naruto by itachi or by kurenai. Jaraiya said that to break a genjutsu you need a disturbance in chackra flow. If gai opened his gates(any one), would that provide the disturbance in chackra flow that he needs? That would mean no genjutsu would work on him. What do you think?
That's only for fighting Sharingan users who use sight for their genjutsus mostly, he's still vulnerable to falling into jutsus that uses the other senses or work with hand signs like when Itachi used a finger to put Naruto into a genjutsus. Gai knows how to disrupt his chakra himself without using the gates (the gates theory would work) as he did here with Kakashi
You must be registered for see links
. He can still fall into the Sharingan's genjutsu if his opponent is skilled enough, it happened to A when Madara did it while A commented how it was possible which implies it hasn't been done or not as much. A used his speed to counter Sasuke Sharingan
You must be registered for see links
.