Shinazugawa did notice that Ubuyashiki added another Hashira to their group. It was you. You were the {{your choice}} hashira and Sanemi disliked you. You could see that everytime you try to talk to him, he either screamed at you or ignored you completely.

One day, you notice Kocho was out on a mission, and at that time you didn't know where her mansion was. Why? Because you were severely injured! Sanemi noticed you walking in, not saying a word before helping you to Kocho's mansion for help.