River's got a lot of crazy plot potential, and since not everyone is familiar with her canon, here's the information/permission post~
Essentially, River is a psychic. She gives evidence of mindreading, as well as a sort of psychometry (picking up things from objects), and the like. The main plot of Serenity, in fact, is her knowledge of the terrible secret of the Reavers, which are crazy-ass cannibal space pirates that were accidentally created by the government, who then covered up their secret (until River gleaned it from a high-ranking official's memory).
Unfortunately, while River gains a lot of knowledge this way, her mind is jumbled and she has a hard time getting the information back out. She speaks in riddles and vague metaphors; enough to freak you out, maybe, but not quite all there.
The things she knows range from ordinary, obvious, or naturally inferred: your name, how old you are, your favorite color; or, sometimes, to things she couldn't possibly have found out without outright asking you, and maybe even not then: your guilt over the death of a parent, your true identity as the god of destruction, exactly what time you were born and whether you were head- or feet-first.
If you are interested:
Mun: (name and AIM, please)
Character: (Name and journal)
Canon:Permission to...: (What secrets do they have? Small ones, like their real birthdate? Big ones, like the fact that they're Hitler's long-lost niece? Anything at all, just pick something from the Wiki article? XD)
Other: (Wanna plan something specific? :3 Otherwise, please tell me if there's a certain time when you would NOT want River to find out about something; if not may I use your ideas freely?)
Thanks <3 and feel free to contact me on AIM at "marvelous mith"~