I can't take credit for this as it was something I was talking about with my friend. but as we were watching DR3, we noticed that izuru often says "tsumaranai/how boring" whenever he sees something that would be particularly traumatizing or frightening to most people. One example is Chisa's brainwashing/torture scene, and another is when the future foundation attack ships are coming to Jabberwock. As we were talking, we theorized that, because of the trauma and torture that Izuru has been through, seeing these traumatic events is likely still traumatizing or distressing, but he will dissociate as a way to cope with seeing these things, since visible emotion and fear were punished out of him during the kamukura project. but he perceives the feeling of dissociation as emptiness or boredom, which is when he will say this. it almost seems like a phrase to ground himself.
