Although other people seem able to guess the identity of the "Friend" at this point (not that dumb shit like Donkey faking his own death or whatever), I'm utterly lost assuming it's not Sadakiyo (and I seriously hope it's not him). Of course there's the "Ghost" incident which still needs to be explained and will undoubtedly become extremely important in "Hindsight". But determining what that might have been is beyond meat this stage. Of course, assuming it's a solvable (or at least guessable) mystery without a last minute culprit never previously mentioned. At this point I'd accept anyone named before this point.