On a cold winter's night, there's a knock at the door of the inn or other lodging where the PCs are staying. Outside is a fresh snowman housing the spirit of a PC's dead loved one: a parent, a child, a beloved. Created just the other day by a young Yemite, the snowman has been drawn here; perhaps by seeing the PC earlier from a roadside hiding place, or by an uncanny urge, or just by one of those one-in-a-million coincidences that seem to happen all the time in a world filled with magic.
The living and the dead have only a short time together, until the next thaw - which may be weeks, days, or as little as a single night. And since one is sustained by warmth, the other by cold, they cannot comfortably share a room or a fire or a snowy meadow, or even touch for more than moments. But much may still pass between them: love, anger, pride, regret, praise, rebuke, and perhaps even reconciliation ... all the things that went unsaid when there was plenty of time to say them.
How does the story end? Does the PC let their loved one wander off into the snow alone to whatever fate awaits them, or do they try to protect the returned one somehow? Does the loved one take matters into their own cold hands to spare the PC from having to make the choice?
Before I Melt Away
In this campaign, the PCs are all snowmen. They might have been practically anyone in life, and their new bodies may be wildly different in size, shape, etc. The one thing that unites them is the simple goal of survival in a land growing warmer and more inhospitable by the day. The coming of spring, once a time of celebration, is now a second death sentence.
There are more immediate perils as well. Few animals find a mouthful of snow appetizing, but they may attack sound and motion anyway, especially if startled. A warm spring rain is like an acid shower. Some children and more than a few adults find cruel sport in threatening snowmen with torches or dismembering them and then leaving the heaped remains to melt into several puddles. (Sure, they scream, but it's not like they're really alive, right?) Most people, however, merely jeer at the unfortunate shades from a distance, or avert their eyes and hurry along, pretending they don't see or hear... anything to avoid having to take pity on the poor thing or face their own mortality.
The PCs will have to come to a consensus on what they want to do. They may decide to attempt the long and dangerous trek to the north, where even if they succeed, their reward is to spend the rest of their existence acting out a heatless parody of their former lives. Perhaps they'll try to find some means of staying cold while the killing summer passes: magic, an ice cellar, or just a nice tall mountain with a shady side. Maybe they'll decide to use the time left to them to resolve unfinished business, seek out loved ones or hated enemies and settle old scores, and so on. Finally, some may decide there's no point in trying to avoid or postpone the inevitable - after all, they already died once - and surrender to the sun's deadly embrace.
The players and GM should go into this campaign knowing that PCs may, and probably will, die along the way. Snowmen are more vulnerable than most heroic characters, and they all have the equivalent of a terminal illness. It's tragedy in the classic sense. This is your fate: do you fight it, succumb to it, or rise to meet it? And what will you learn about yourself and the world before the end comes?