If you are flying to Japan, first thing you have to do before arriving at your nearest airport is to check the weight of your luggage. Major airlines allow maximum 23 kg or 50 lb per checked luggage for flights to Japan. Then, if the weight exceed 23 kg, you have to pay a supplement for the overweight or you have to pull out your items from the suitcase and replace into your cabin luggage.
Usually the large size suitcase weigh around 5 kg and therefore you can put in up to 18 kg to your suitcase. Then, do not fill up your suitcase without any space when leaving your home. Most of the travelers will buy souvenirs in Japan and the items inside the suitcases will increase upon return flights. Therefore I suggest to fill up only 70% of the luggage and do not forget to put a foldable bag inside the suitcase. This foldable bag can be used upon return flight, placed with items which were unable to be put inside your suitcase due to capacity or weight limit.