Yea only for sensors with short range. The only other way itachi's genjutsu could catch a sensor is if they were distracted like what sasuke did to to C in his battle with the forth. Other than that sensory is your best friend against guys like itachi.
Not exactly. 1 if his sensory focused on sasuke still, Cee would've had the time to break it not avoid it. To counter genjutsu you have to avoid it, the luxury of getting caught in it and to be skilled enough to break it before getting killed is very unlikely. in Cee's case, he was already subdued by it's power. samething happened with orochimaru but itachi sliced his hand off. 2. Distractions works in itachi's favor. if he was able to fool a sensor with crows just enough time to grab sasuke's sword and cut his horn then he would've had more than enough time to catch him in genjutsu if kabuto's eyes were open.
The way some people think, it's like Itachi doesn't follow NV physics...
Every Jutsu requires molding of chakra one way or another, and that build-up can be sensed by any good sensory type. And MS Jutsu are kind of very noticeable, even non sensory types feel the stuff going on.
sense chakra knead =/= sense when it's used.
- if you're talking about amaterasu, assuming juubito sensed instead of "see" the chakra form into sasuke's eye, that doesn't apply to genjutsu since you'd still not know when it's coming unlike amaterasu. and like you said, non sensors could feel the technique being formed but all of those moments was about amaterasu likely because out of all the dojutsu techniques with exception to susanoo, the flames itself is nothing but chakra, powerful chakra at that.
No you are wrong here OP. chakra build up for genjutsu can be sensed.It's proof is in the manga. Nagato sensed it during itachi/nagato vs naruto/bee fight. He just thought it was amaterasu. But it was genjutsu. That proves he sensed genjutsu. Kabuto was over cautious, since he considered itachi too be very capable ninja which he was obviously. But kabuto both overestimated and underestimated him. He just took extra precaution, and that's who kabuto is. Kabuto is always cautious throughout the manga. But he didn't consider the possibility of a genjutsu that wouldn't need eye contact, and that was his undoing. Since he didn't consider this possibility, he wouldn't know what the chakra build up for said jutsu was. Just like nagato didn't know if it was amaterasu or genjutsu. Though it's unclear whether izanami even requires chakra since it takes an eye. Same is the case with izanagi. I doubt they even use chakra.
That doesn't make sense, Itachi didn't use genjutsu either when nagato "sensed"
Yes izanami use chakra, karin noted a dip in danzo's chakra each time he used izanagi.
kun: