Heirun has weather-browned skin with a dry, fine-grained texture from years of kiln heat and windblown grit. His jaw is broad and slightly lopsided from a childhood habit of chewing hard resin; when he laughs, his square teeth show in a sudden, startlingly boyish grin. He moves with a careful, measured step, as though every floor might be a diagram he has not finished reading. A thin halo of soot often settles along his hairline, and his sleeves smell faintly of wet slate. Unexpectedly for a young mage, he keeps a tiny paper windmill tucked behind one ear and turns it whenever he is thinking.

Heirun is resourceful and generous with his labor, yet prickly when anyone calls him brave. In a crisis he becomes brisk and decisive; in a classroom he is restless, argumentative, and liable to challenge a rule with a better method. When relaxed, he is dryly funny and fond of small mechanical toys. When tired, he grows controlling, trying to solve everyone else's problems before they can refuse his help.

Heirun was raised in the kiln district of Siltstep, where his family fired roof tiles and repaired storm-damaged chimneys. As a boy, he could tell a bad draft by the taste of the air. A traveling mage noticed this knack and brought him to study at the House Above the Ford, an old observatory built over a flood channel. Heirun proved brilliant at practical wards and poor at reciting doctrine. The formative turn came during the Siltstep kiln fire: an instructor ordered him to hold a containment circle until help arrived, but Heirun broke the circle to pull his trapped younger cousin, Nemi, from a collapsing shed. The fire spread into the district, killing no one but destroying three workshops. He still believes he made the right choice, though his school calls it a failure of discipline. He now apprentices under Master Tovashi, who is protective in private and exacting in public. Heirun sends most of his pay home, while quietly trying to discover why the fire's first flame burned blue.