Yoisho commands a crew of sailor mice operating from the harbor. Kind-hearted and highly reliable, he maintains a calmer disposition than companions like Gamba. A distinct physical feature is his missing right eye, lost to an injury directly inflicted by the antagonist Noroi; this wound stands as a constant reminder of past clashes. He shares a lifelong bond with his childhood friend, Gakusha, shaping their established dynamic. Yoisho also has a romantic partner named Yuri.

His role centers on providing steadfast leadership and support during the crucial journey to Yumemishima. He commits to Gamba’s quest to defend the island's inhabitants against the Noroi Clan, lending his experience and steady nature to the collective effort. This dependability solidifies his position as a key figure within the adventuring group.

In subsequent adaptations, including the 2015 film, Yoisho's core traits remain intact: his leadership role, missing eye, and calm demeanor. His presence endures as part of the core group confronting the threat posed by Noroi and his forces.