Seli has the rangy, weather-hardened look of someone shaped by years at sea. Fine, opalescent scales stipple her temples, collarbones, and the backs of her hands, catching light like fish scales seen through shallow water. She moves with a measured side-to-side roll even on dry land, as though quietly compensating for a deck's sway. Within a minute of meeting her, most people notice her thumb repeatedly checking the small brass ring threaded through her belt, a habit she barely knows she has. Unexpectedly for a celebrated navigator, she keeps a tiny, meticulously tended sprig of shore thyme tucked into her chart case.

Seli is daring when a route needs testing, but cautious when a decision could endanger someone else's crew. She is proud of her skill and impatient with sloppy thinking, yet uncomfortable with the fame it has brought her. In a crisis she becomes brisk and commanding; afterward, she may fuss over a stranger's wet sleeves rather than talk about her own fear.

Seli grew up on a working skiff among the Sirenkin, learning to read the sea from her mother, a net-mender who judged currents by how a line trembled through her fingers. Seli's first charts were scraps of sailcloth marked with charcoal. When a chain of volcanic vents rose without warning across a busy passage, the old route became a field of boiling water, poisonous bubbles, and new reefs. During the first rescue attempt, Seli's younger brother Thes vanished when their captain ordered the boat onward rather than turn back for a trapped crew. Seli disobeyed, found a narrow passage by listening to the pitch of bubbles against her hull, and brought several survivors home. The route made her famous, but the loss and her disobedience left a permanent fracture between her and the captain, now her former mentor. She still charts the vents as they shift, while trying to persuade the harbor council to mark the passage for ordinary sailors instead of keeping it as a guarded commercial secret. Her mother, Hessa, sends her thyme sprigs with every message, and the rescued pilot Besh has become her most dependable, if argumentative, co-navigator.