Shioji hails from Yumemishima Island, part of its community of mice. She is the granddaughter of Elder Shuro, the island colony's leader, and acts as an older sister to Chūta. Her peaceful life shatters when Noroi and his weasel clan invade her homeland, devastating the inhabitants and disrupting their existence.
Noroi captures Shioji during the conflict, making her pivotal to the struggle. This kidnapping serves as Noroi's strategic move to control the island's remaining population. Her captivity directly motivates the rescue mission led by Gamba and the recruited mice forces, positioning her centrally in the conflict against the weasel clan.
While imprisoned, Shioji endures confinement resiliently as Noroi uses her for leverage. Her plight intensifies the urgency for the protagonists to confront Noroi, directly driving the narrative toward the climactic battle. Her eventual rescue helps unify the island's defenders against their common threat.
Following her rescue, Shioji joins the collective effort to reclaim Yumemishima. Her actions support the broader defensive strategy, though specific tactical contributions aren't detailed. Her presence reinforces the narrative focus on communal resistance and the protection of her homeland alongside her brother and fellow defenders.