So, this is an idea that I've had flitting around my head for a while. It's still got a lot of blank spaces in it; hopefully someone can help me fill those in.
The premise, as I see it so far, is that the ghost of a woman is haunting a dwelling of some sort; house or apartment. She is invisible, intangible, and has limited ability to interact with the world of the living. She does have some typical ghostly powers (the exact nature of which can be discussed), but living people never seem to notice; if she moves an object, for example, they tend to think that they moved it earlier and forgot, and she can't seem to move objects when people are actually looking. Any attempts to communicate have failed.
And then, a new tenant moves in, a young man.
One of the abilities of the ghost is to enter people's dreams. This is only for watching, as the dreamer never reacts to her in any way. Except... this new tenant does. He sees her, talks to her, totally unaware that he is dreaming. When we wakes, the dream fades, just as any other dream does. But bit by bit, he'll remember aspects of it. As time passes, and more dreams come, he becomes more aware of her as a presence in his dreams, and more aware of her outside of them as well, gradually being able to see her and interact with her while awake.
That's the basic premise. As I said, there's still a lot that can be filled in. For example:
The ghost: Who was she when she was alive? How did she die? Does she remember either of these things? One direction that the story could take is that the tenant helps her to find these things out. What keeps her from letting go?
The tenant: Who is he? Why can he interact with the ghost, when no one else can? Perhaps he has some past connection with her. Probably not having known her, but something else; he could be the descendant of someone who she knew. Perhaps someone he knew died with her, and the two of them were linked. For darker possibilities (which are not my first choice), perhaps he knew her killer, instead. Perhaps he had some sort of traumatic experience. Perhaps he's just creative and artistic.
What happens: The basic premise is above. What happens from there? I mention one possibility, that the tenant helps the ghost rediscover herself. Another is that he helps her move on. Perhaps, somehow, they end up bridging the gap between them, either his continued belief and love bringing her back, or him gradually fading away, joining her in the afterlife. Do they go places, in the world of the living or the dead? Is there conflict of some sort? Maybe there is someone, a living girl for a love triangle, or perhaps someone from the ghost's past is making trouble somehow.
Anyway! Clearly, there's a lot to discuss. If you think that the idea is interesting, and you'd like to work out some of the details above, send me a PM! I should add that I see this as mostly being a fairly light, romantic roleplay, despite the fact that one of the protagonists is dead. I like humor, so that's almost certainly going to come up from time to time. Further, I should add that I am very squeamish, so I would hope that we would stay away from anything icky, using a very broad definition of icky.
Thanks for reading!
EDIT: Note that I wrote the idea with particular genders, but there's no reason that the roles can't be reversed, with a male ghost and female tenant.