Ghosts, What are they? Options

[Tashiro]

So, I've got a character in this campaign with a bit of a weird background, and I'm trying to make sure things are on the up-and-up. Specifically, the character was part of a matched set, and his sister died. We have his sister haunting / possessing him, and so far we're using the Free Spirit character rules, which works reasonably well (Free Guardian Spirit). But the thing is -- is that the most appropriate out of the mix? It sort of fits with Shinto -- once a person dies, if you perform proper rites they become ancestor kami and don't go to the underworld, but I'm wondering how this works in 4E.

Specifically, I don't see any rules for ghosts in 4E so far -- or am I just being blind as a bat?

So, are ghosts now just a type of specific spirit? I'm wondering -- if ghosts are, then fine. If they aren't, I can half-imagine a free spirit deciding to take on the form of his deceased sister as either part of some elaborate plot, or out of sympathy, or something else. He's openly willing to let her possess him, and I can see a free spirit using this to their advantage, but I'm curious about the actual 'canon' rules for ghosts in 4E.

Opinions welcome.