Karos is a massive Jotun-Kin whose skin resembles dark furnace tile, split by fine orange seams that brighten when he exerts himself. Obsidian spines rise along his shoulders and back, scraping softly against the uneven fit of his soot-stiffened coat. He walks with a deliberate, heel-first weight that makes loose grit jump. His left pauldron is polished nearly smooth, while the rest of his armor is patched with mismatched rivets. Though he commands a feared patrol, he keeps a little clay cup tucked into his belt and carefully waters a tiny, heat-loving sprout whenever the Guard camps near a vent.

He is blunt enough to make allies wince, yet patient when someone is honestly trying to understand a dangerous system. In a patrol dispute he is forceful and quick to decide; with frightened workers he gives them time and simple instructions. He distrusts grand promises but is unexpectedly careful with small living things.

Karos grew up among the vent-tending families of the Primordial Magma-Forged, where survival depended on sharing warning before a seabed passage collapsed. As a young guard, he believed every trespasser was an enemy. During the Siltfall, a sudden failure in an old siphon passage trapped his sister, Salla, and a rival family's crew on opposite sides of a flooding vent. Karos broke his own patrol line to lead both groups out through a narrow basalt throat, losing several people when the passage shifted behind them. That day changed his idea of strength: he still meets threats head-on, but now insists that every danger be announced to all who depend on the vent, even adversaries. He commands the Cinder Guard along the Boiling Arc and is locked in a worsening dispute with mining interests whose machines are disturbing the rift. Salla, now a route-choir caller, thinks his patrols are becoming a wall where a warning system should be.