He has an undying love for fire. He craves the heat and only feels at peace when he's engulfed in flames. His skin never blisters or shows the slightest sign of discomfort when he sneaks off into the woods to feed his addiction.
When the cold sets in, he feels an aching pain in his chest. Fin can't let anyone find out. Others have been burned in the village square for less.
A small part of him wants them to catch him and burn him just so he can know what it's like to be surrounded by fire...