An ice pixie and an Unseen University student, class of 1182. She is a tiny humanoid mostly hidden by the cold and light she puts out. She has zero understanding of human society and reacts to this by studying everything and trying to follow all the rules.  She is majoring in arcane sciences.

Description by Trissiny, chapter 2-6:

"Fross was about three inches tall, and…fuzzy. She looked something like an anthropomorphic white moth, her humanoid figure coated in white down that glittered like snow in the starlight, with reddish highlights where it caught even the glow of the distant campfire. Her eyes were enormous (proportionately) black jewels that dominated her head, leaving no room for anything else on her face but a thin little mouth and two arched, fuzzy moth antennae. From her back sprang four wings, long and narrow like a dragonfly’s, but without the network of veins. In fact, they were all but invisible except for their frosted edges. They buzzed in short bursts, apparently unwilling to be still even when Fross wasn’t flying."