Smokey brown cockroaches (kurogokiburi) are said to prefer living outdoors, but we sometimes get them in our house. They are scavengers and will eat almost anything but normally feed on plant material. Fast moving and quite large (3cm) with spiky legs, they terrify many people, who claim that they are incredibly dirty and dangerous. Of course they may carry some germs, but these creatures are no dirtier than many other things around us, such as the pet dog that you allow to lick your hand (or face!) after he’s licked his backside! The fear of cockroaches is really quite irrational, since they cannot hurt us by stinging or biting, and we can always wash our hands after picking one up.
By the way, there are around 50 species of cockroach in Japan (but only 6 species are very common).
Good website on cockroaches: http://www.bio.umass.edu/biology/kunkel/cockroach.html
Insecta: Pterygota: Blattodea: Periplaneta fuliginosa (kurogokiburi)