Zushiohmaru Sumida serves as a loyal canine companion to a central figure, initially appearing as an unassuming pet. Beneath this role lies a concealed history: he once served as an experimental subject in developing the Slave Control Method (SCM), a controversial animal-control device engineered by Dr. Sumida. These trials occurred prior to his reunion with his current owner, who remains oblivious to his clandestine past as a test subject. Fleeting flashbacks hint at his life before reunification, though precise circumstances remain shrouded. His ordeal illuminates foundational aspects of SCM’s functionality, yet his direct impact on its operational use or broader narrative implications stays deliberately undefined, preserving an enigmatic link to the system’s mechanics.