Rusui officers of domains were also called Oshirozukai (literally, an officer at the castle) in Edo, established a Rusui association approved by the bakufu to exchange information, and therefore, they were so-called diplomats of domains.
江戸で諸藩の留守居役は御城使とも言われ、幕府公認の留守居組合をつくって情報交換をしており、いわば諸藩の外交官であった。