Jack has wind-paled skin with a faint, rosy flush across her nose and cheeks, and hair the color of thawing snow, tousled into short, unruly waves. Fine ice crystals sometimes cling to the ends even indoors. Her clear blue eyes crinkle quickly when she laughs, though they become watchful when anyone speaks of an endless winter. She moves with the loose, gliding balance of someone who learned to walk on frozen rivers; when she stops, she plants her staff as though testing the ground for a hidden current. She smells unmistakably of crushed mint and cold stone, a scent she knows about and insists comes from her coat. The unexpected detail: beneath her winter layers she wears a bright, patched summer apron, embroidered with tiny yellow pears, which she puts on whenever she cooks.

Jack is welcoming and irreverent with common folk, but more cautious than her easy laughter suggests. In council she listens patiently until she senses someone being cornered, then becomes stubborn and blunt. When relaxed, she jokes, cooks, and invites people to race across frozen ponds. When afraid, she overplans and tries to solve everyone's trouble herself. She loves winter fiercely, but refuses to treat it as an excuse for cruelty or permanence.

Jack was once a seasonal spirit whose work was to bring the first hard frost to the valleys around the Sleet Ford, preserving orchards and giving the soil a resting season. Ciena met her during a winter when a late blight threatened the region's pear trees. Jack diverted a frost meant for the orchard into an abandoned quarry, saving the harvest but trapping herself beneath the ice until Ciena led a rescue. Their friendship began over a shared pot of pear stew, and years later they became co-rulers of the Frost Marches. Jack's formative change came when a desperate council begged her to make winter permanent, believing an unchanging season would end famine and war. She agreed for one terrible year. Crops failed, travelers vanished, and even her own people forgot what thaw felt like. She broke the spell with Ciena's help and has since believed that winter is a gift only when it knows how to end. Now she and Ciena govern together, but their methods clash: Ciena favors firm decrees, while Jack prefers negotiation and public feasts. Jack is trying to repair a damaged succession pact with the neighboring thaw-vales while keeping the council from using the old winter spell again.