This one gave me the willies when I read it the other day. Having a demented Japanese woman lurking in a dark corner of your house would be creepy no matter what, but after seeing Ju-on it's REALLY creepy.
Only difference is that this woman wasn't lurking and killing people but I digress. If you come down to it, there's all kinds of technical and operational issues here that immediately come to mind.
So...she was hiding in the closet for about a year. Now if the guy was single and living there alone, and it does sound like he may have been, I can understand her having the run of the place during the day when he's out to work.
But at night...all I can say is this guy must sleep like a brick. I don't know how the nooks and crannies in a typical Japanese house are arranged, but there's only one place where I live where someone could conceivably pull this off and that's the attic (no basement).
Thing is, I'm a nightowl and if something of appreciable mass was moving around in the attic, I'll find out about it. But in this guy's case, she was in 'a flat storage space only just big enough for a person to squeeze into lying down'. So was she lying perfectly still in there all night? I tend to think that unless you're a fucking ninja or something (no stereotyping intended) that you'd lack the sanity or discipline to do that.
And so she'd have to stay in this place all the time while he was there, so what if she needed to take a bio? She had plastic bottles in there, was she pissing in them at night? And was this closet in the dude's room, or elsewhere in the house? because in the former case, then was she lying there watching him?
I mean, this is fucking creepy. All I can figure, with what I know, she was either real good, or lucky, or he was just plain bad for her to be there nearly a year before he figured shit out.