[quote]It should be noted that the characters we play DO NOT know what the thing within their mind is; indeed they are not even aware that it is a separate soul within them. Their failed twin's soul, who has been with them from even before birth, is none the wiser. (For now.) Some of the host twins don't even know that they had a failed twin. All that our characters do know is that there has always been someone else there, present but intangible, and powerful enough to move and attack things without a body. Our characters also possess the ability to see spirits.
[/quote]

The thing is, they just don't know what the thing is. They know there's a voice in there, and that its something beyond normal, something that can see and think and somehow move things on its own. They just don't know the "what" factor. [i]What[/i] is this other sentient thing? Remember, many of them will have grown up with this thing in their head, probably thinking [i]its perfectly normal[/i]. They don't start out having a name for it...its just another thing there in their head; a weird extension of themselves. A good deal of them, when they found out it wasn't normal, probably believed they were crazy, or that they'd got some type of mental disease or syndrome. Many of them would probably think of it as a second conscious, now, at the stage of life that they're at. 

So I mean, they are very well aware of the "other person", just not [i]what[/i] the other person is.