also I wasn’t going to venture into the 112 confrontation because I’ve been trying to talk about things other than kurofai (FOR ONCE IN MY LIFE HAHAHAHA /rolls under the shame table) but. let me just cry a moment.
during infinity, we see kurogane starting to express the fact that he’s genuinely pissed off about fai’s emotional reticence and attempts to act on his own (and, by extension, at sakura’s similar behaviour, because cool more explicit fai and sakura parallels). kurogane is that guy who watches romcoms and yells “TALK TO EACH OTHER FFS YOU COULD SAVE YOURSELVES FORTY MINUTES OF ANGST IF YOU JUST SAT DOWN AND HAD AN HONEST CONVERSATION”. he dislikes the idea of being locked out of the loop, and he hates the idea that fai is hiding things from him and trying to operate on his own.
THE PROBLEM WITH THAT IS that for kurogane, the confrontation pictured above is communication? he struggles with subtlety and with sincere expression. instead of saying “I want to trust you and I want to keep us all safe and I don’t care what you’ve done in the past so please just go sing the Frozen soundtrack in the shower twelve times or whatever it takes for you to let it go”, he uses physical force and yells “GET YOUR SHIT TOGETHER”. I honestly think it’s directly tied to his arc of understanding that strength alone isn’t always the answer - he needs to understand that sometimes, anger and brashness actually just cannot get you anywhere? he’s trying to communicate with fai, but he’s still approaching that communication from entirely the wrong angle.
and we know that his approach doesn’t work with fai because almost directly after this confrontation (srsly it’s their next scene together), fai and kurogane come to the joint realisation that something is going terribly terribly wrong with syaoran. fai’s course of action? the standard ff.net diversionary tactic of hiding the pain in his tortured cerulean orbs behind a mask of icy smiles or whatever, and then his attempt to get syaoran as far away from the building as he can. fai knows exactly what is going to happen, but he cannot tell kurogane for fear of compromising his position, so he tries to deal with the problem on his own.
kurogane is left alone with sakura, darkly muttering about fai, partially because yeah, he wanted in on the mutant worm-hunt, but also because he doesn’t understand fai’s reasons for locking him out of the loop - and fai, in addition to being committed to his primary goal of resurrecting his brother, similarly doesn’t understand that kurogane is genuinely concerned about him, and continues to operate alone? which is why, surprise surprise, arm-grabbing and irritable capslock, despite being a sincere attempt at communication, do not work.
I do find it interesting that a lot of their most significant moments of genuine communication that happen later do actually involve physical violence - fai picks up kurogane’s habit of head-bops in nihon and in clow loop and uses them as a means of emotional expression, which to me is what shows that he’s figured out kurogane’s particular method of communication and has realised that kurogane cares about him. so there’s that too.
So what you are basically saying is that after 6 months in Yama, Fai managed to not pick up even the basics of Kurogane’s language.