As far as I know huntsmen and other big spiders are common throughout Japan and yes they can get inside...they can all get inside. The following are the avoidance techniques you should use to limit this:
1 Close the windows and sliding doors. Your sliding doors will have screens designed to keep out insects. These will NOT keep out big spiders, which can push through the black fringe at the edges of the screen door. If you want to keep spiders out you need to keep the door properly closed at all times.
2 Bleach your drains. You will probably find that you're bathroom is a wet-room, covered in tile with a big drain in the centre of the floor. Those are big holes aren't they? You'd be surprised what can fit up there. Pour bleach down it often and cover if with something heavy while you're not using the shower. I use a brick. You should also bleach all your other sink drains.
3 Secure the fan. If you have a gas cooker, there will be a wall fan above it. This tends to have large spaces between the blades and though it may have a cover on the outside, it's pliable so stuff can get through. This may sound crazy, but I stuck a large plastic basket on the wall over my fan. It has tiny holes, through which I fed the fan cord so that I can still turn it on and off. I've yet to find a huntsman sitting in there waiting for me and I don't know what I'd do if I did...turn on the fan? Regardless, it gives me piece of mind.
4 Keep your house/apartment really clean. If you get little bugs, you will get bigger bugs, and then the biggest bugs. Keep your rubbish outside if possible. Keep food smells to a minimum. Clean up spills etc asap. If you see little bugs, worry, eradicate them. If you see cockroaches, really worry...huntsmen eat these.