Sanna is very small, with a restless, spring-loaded way of moving: she bounces on her toes, darts sideways around people, and seems to lean into turns before deciding to take them. Her grin shows a tiny gap between her front teeth, and when she concentrates she worries her lower lip with them. Her short red hair is tied into a rough ponytail that keeps shedding wisps around her ears. Her fierce green eyes look bright with ideas even when she is exhausted. She is often smudged with soot and smells faintly of hot iron, salt air, and the sharp tang of lamp oil. The unexpected thing is that she has an excellent memory for other people's favorite snacks and quietly leaves them where they will be found.

Sanna is exuberant and quick to trust a fascinating mechanism, but wary of strangers who ask about her family. She can be funny, generous, and impossible to keep still; in moments of genuine distress, the chatter vanishes and a serious, watchful child takes its place. She wants people to admire her inventions, yet hates being treated as a spectacle. Her confidence is real, but it often covers fear that the people she loves can disappear without warning.

Sanna's parents were killed by bandits when she was very young. She remembers the noise more clearly than the faces: boots on wet stone, a cart horse screaming, and her mother's hand pushing her beneath a broken fish stall. Her uncle took her in and raised her above his blacksmith shop in Feasgar, where she grew up among bellows, harbor gulls, and half-repaired tools. When she was nine, she built a wheezing little clockwork dog from scrap and named it Maxwell. She kept improving it until it could carry her through the streets, then unfold into a scavenged mechanical houndframe she can wear. At eleven, an experiment with a powder charge blew out a shop window and started a fire in a sailmaker's loft. Her uncle helped her repair the damage, but made her swear to test dangerous inventions at the abandoned quarry beyond the city. She tries to keep that promise, with inconsistent results. Now she is building a more reliable power core for Maxwell while helping at the forge and dodging city inspectors. Her uncle worries that her frantic cheer is a shield over grief she has never learned to carry.