>>283668458
>>283668489
I think that in Preparation, some of the members weren't convinced to defect but were actually planted in the Kamunabi since the war.
There's also the Hishaku spreading the rumors about what actually happened during the war but I don't know if it was only to undermine Samura's mental health or it had some extra purpose since I remember Yura said that it had "failed."
The plan is pretty solid, with the exception of some stuff like why he kept Chihiro alive and Hakuri being a big wrench if he manages to get to another sword bearer.