Shijin is a doctor mouse traveling with Gamba's companions. When intoxicated, he habitually recites poetry aloud. His highly sensitive ears detect sounds beyond the range of others, providing crucial tactical advantages during the group's journey and confrontations. Shijin joined Gamba's mission to defend Yumemishima Island after finding the injured Chūta at the harbor. He journeys alongside the core group, including Yoisho, Gakusha, Ikasama, Bobo, and Gamba. Shijin's vital medical expertise consistently aids the group's survival through numerous challenges faced on their voyage.