Chester is an insular mouse from the island of Yumemishima, the younger brother of Shioji and grandson of the island's elder mouse, Shuro. His homeland suffered invasion by the cruel weasel clan led by Noroi, plunging its inhabitants into hardship. Injured during the conflict, Chester barely escaped the island. He journeyed seeking external aid, arriving at a harbor where he encountered Gavin (Gamba) and his companion Matthew (Mampuku). Chester presented a desperate plea for help to defend his family and fellow islanders against Noroi's ongoing oppression. His appeal successfully convinced Gavin to recruit a crew of sailor mice for a rescue mission. Chester joined the group as they stowed away on a boat bound for Yumemishima, providing vital information about the island's dangers and Noroi's tactics during the voyage. His character involvement centers on motivating the central adventure to confront the Noroi Clan and liberate his homeland.