There are lot of online hotel booking site to travel the world Expedia, agoda, Booking com. etc. But if your are planning a trip to Japan, why don't you find from Japanese local online booking site? Some hotels or ryokans are more cost lower than major booking sites, and also you can find some unique accommodation. Maybe you have seen before on the tripadvisor or somewhere but wasn't it hard to reach your preferred language site? If you are interested here below you can reach the international site. (Go through from the characters)
Have a nice trip!
To help you to buy stuff direct from Japan through Japan's largest and well known online shop Rakuten and amazon.jp