Sethri's Oread heritage shows in the fine, stone-grain ridges along her temples and the faint mineral sheen of her skin, like damp slate under lanternlight. Her jaw is broad and sharply jointed; when she chews, the muscles work in precise little pulses, and her square, slightly pointed teeth show whenever she laughs at a result she did not expect. She moves with quick, economical steps, pausing to feel the floor through her soles before crossing a room. The detail people least expect from the Measurers' severe leader is a small brass wind-up beetle clipped to her collar, which she repairs and oils with devoted care.

Sethri is intensely curious and deeply considerate, yet her care often arrives disguised as a checklist. She can listen patiently to a frightened novice, then become impatient with an expert who skips a step. In private she admits doubt; in front of the Unsealers she argues with exacting confidence, partly to protect her faction and partly to keep herself from wavering.

Sethri grew up between human surveyors and Oread stonewrights, learning early that a crack has a history and that a good measurement can prevent an argument from becoming a burial. She joined the Tectonic Cults to study the knocks that began echoing through the catacombs, expecting ritual metaphor and finding instead a pattern too regular to dismiss. Years ago, during a survey beneath Hush-Rock Hollow, she trusted a veteran's confident reading over her own unsettled calculations. A passage failed, killing her mentor and injuring several workers. Since then, she records every uncertainty as carefully as every result. She became the Measurers' leader because she could translate their observations into terms even rival factions understood. Now she is trying to stop the Unsealers from forcing the Ring open while keeping the cults from splitting into enemies. Her closest working ally is a Keeper who supplies access to the catacombs; Sethri has not told them how often she doubts her own interpretation.