Millie Caliver is the younger sister of Sadie Caliver. The sisters live together in a cabin built by their father, located within a forest. When soldiers search the woods for an escaped individual named Miu, Millie helps her sister Sadie hide Miu after Sadie finds her unconscious. Millie flees with Sadie and Miu through snowy terrain, using a nearby stream to cover their tracks and evade the pursuing soldiers. She then travels with Sadie and Miu back to Miu's home village, where they discover Miu suffers from amnesia.