Rusui officers, being under control of Roju (the second-highest post in the bakufu government), controlled O-oku (inner halls of the Edo castle), managed the travel certificates, and played the role of guarding the Edo castle while Seii taishogun (literally, "the great general who was to subdue the barbarians") was out of the castle.
幕府における留守居は、老中の支配に属し、大奥の取り締まりや通行手形の管理、征夷大将軍不在時には江戸城の留守を守る役割を果たした。