I'm new to this site but I couldn't resist throwing in my 2 cents after reading through everyone's posts...I lived in Hawaii for 3 years and cockroaches are an everyday occurence--i've had them on my floors, my walls, fly into the side of my face, scare me when i'm brushing my teeth and i see their feelers poking out of the hole in the side of the sink. They were a little scary sometimes but I wasn't about to flee the islands because of it. If anything, I just got mad and tried to force them outside, if that didn't work, i killed them. I've never been to Japan but last summer I was in Thailand and I didn't see any cockroaches the entire time I was there, which i found kind of amazing....
I was in Japan for two months a few years ago and I travelled all around and I can't remember seeing any cockroaches when I was there. Maybe it's worse in the summer but when I was there (October/November) there didn't seem to be a problem.
One thing to remember, they were here before us and will most probably go on to live after we are gone...
you will have to try and get used to them, but I suppose you could avoid your chances of running in to them by gettin better accommodation...
I don't recall seeing any cockroaches in any of the places i stayed in in Japan - the hostels do tend to be fairly good quality so you should be ok. My friend lived in Fukuoka for 2 years and i don't remember her ever mentioning anything about cockroaches, and i know she is not keen on creepy crawlies.
I stayed in Kyoto for a month for a summer language program (Here to be exact http://www.kyoto-apartment.com/kap1/facility_flatshare_e.htm) where I saw my very first cockroach. I was SERIOUSLY horrified. My Korean roommate was also terrified since the ones in our building were apparently 3-5x bigger than ones she'd seen in Korea. Roaches were almost EVERYWHERE in that building, especially the laundry room and front entrance. We sprayed regularly, got "gokiburi hoihoi" (little bait stations with poison), and after that only saw them outside and when we did our laundry for the remainder of the month.
After that, I stayed in fairly rural Yaizu in Shizuoka prefecture for about 2 weeks with my boyfriend in his family's apartment where I did not see a SINGLE roach. None in their apartment, none dead on the sidewalk, none anywhere that I saw. I also saw no roaches at my Host family's very old, traditional style house in rural Nara. Given this, I'm sort of inclined to think they're more so an issue in the more cramped urban centers and really old buildings (which the Kyoto apartment certainly is).
I'm moving to Shizuoka this December, and I won't lie, I'm still terrified of roaches and will cry my eyes out and call my mom back in Canada every time I see one
However, even though I didn't see any in rural areas, I know they're there. So arm yourself with some spray, maybe some hoihoi and wish for the best since Japan is far too awesome to miss for fear of creepy-crawlies Good luck!