One of the townsfolk has felt a bit under the weather of late. It all started when someone noted that they looked a bit pale, but now it seems all their color is beginning to fade. In fact, as time goes on, the person is beginning to fade from sight. What can they do about this strange phenomenon, and what transpires as more time passes?
Ideas and questions:
Perhaps among regular symptoms, there are other things that are beginning to become apparent as well. The townsfolk might have a ravenous appetite, or might have odd visions.
You could make it so that the invisibility is more than it seems. Perhaps they aren’t merely turning invisible, but are bridging a gap between worlds, and once they fully disappear, they end up in a different plane of existence.
As the person begins to become less and less substantial, do their initial symptoms begin to go away? Or do they continue to get worse?
Is it possible that this affliction is contagious? Do other people in the town begin to fade as well? If so, what is causing the contagion, and is there any way to reverse it?
Did the townsfolk who has come under this rare case do anything recently that could lead others to the truth of what had happened? Did they come into contact with any magical artifacts, or venture to any places where strange things transpire?
Take your character to the end of the affliction—or at least, the first phase of it. Write what happens when they first become fully invisible, and what transpires afterward.