Rose's of the Forgotten

Kashuu always got eager when his saniwa called him up to his room. It meant the uchigatana was going to be heading out on a mission, or that he would be getting spoiled in some way. So why was this time different? Why was it that when his saniwa told him the details regarding this particular mission it bothered him? Was it the fact that it was in an alternate universe connected to theirs? Or was it that Kashuu had to do this mission as a solo?