Wumi is a broad, salt-weathered human with a compact build and the steady, rolling balance of someone accustomed to decks that never quite stop moving. Their brown skin is stippled with pale freckles from years on open water, and their black hair is cut close at the sides but left in a short, unruly crest that catches spray. A small brass washer hangs from one ear, an ordinary tool part polished smooth by years of fidgeting. They wait with their weight on the balls of their feet, toes turned slightly toward the nearest exit or gangplank. In a room, their eyes go first to the windows, then to the floorboards, as if checking what the building is saying. The unexpected detail: Wumi keeps a tiny, carefully mended paper theater tucked inside their coat and makes shadow puppets for children during long waits.

Wumi is cautious about people but impulsive about mysteries. They can be patient and observant when a crew member is frightened, yet stubbornly restless when an unexplained sound or pattern presents itself. In good spirits they are wry and generous with stories; under pressure they become brisk, practical, and hard to interrupt. They dislike being treated as a hero and secretly enjoy being the person everyone asks for a way through.

Wumi grew up among the mudflats of Bellows Reach, where their mother repaired skiffs and their father kept tide tables for the harbor pilots. As a teenager, Wumi joined a government survey launch whose crew found a drowned shrine beneath a reef shelf. During the first dive, a pressure shift trapped two divers in a flooded passage. Wumi heard a repeated, almost musical knock through the rock and persuaded the crew to cut through a wall rather than follow the official route. The divers survived, but the survey captain falsified the report to protect his contract. Wumi quit and became a freelance sounder. Years later, they joined the crew called Ninth Sound, named for a misnumbered naval survey mark, to find the shrine's resonant stones. Wumi is connected to Pahru, a former crewmate and trusted friend who now wants the stones removed before they can be claimed by salvagers. Their disagreement is personal: Wumi believes the stones may reveal why the old shrine was sealed; Pahru fears another expedition will kill someone. Wumi sends part of every season's pay to their mother and has been quietly covering the costs of a crewmate's debt.