For the Muslims in Japan as well as the foreign Muslim tourists to this island nation, it is important to make sure that they are actually consuming 100% Halal food/meat while roaming here and there in different parts of the country.
In fact, the above statement is harder than it sounds. It is difficult to regulate either by the Japanese Government or the various Halal certifying bodies spread all over the country. At the end of the day, it is the meat or food seller who can or must make sure that he actually provides halal meat or other food items to his customers all the time.
The problem with most of the Halal meat in Japan is that it comes from countries such as Australia, New Zealand or Brazil. So, even for the local Halal food/meat suppliers, it becomes difficult to visit farms and slaughterhouses, often located in foreign lands, to make sure the animals are being slaughtered according to the most common Shariah standards given by the Sharia scholars of the present and the past.
There might be some meat suppliers or wholesalers who would want to mix halal meat with non-Halal one as the later is little cheaper that the former.
I personally got a chance to meet some so-called halal restaurant owners who follow the same practice of mixing Halal meat with the non-Halal one just to get some extra money. They do not even bother to buy Halal soy sauce or halal spices as they are expensive than the non-Halal ones.
There are some groups of Muslims who even value how animals are treated before they are slaughtered as much as how they are slaughtered.
Another group of Muslims thinks that the meat imported from Australia is Halal while the chicken from Brazil is not.
Some slaughterhouses in the country have already started slaughtering animals according to Islamic Shariah standards. However, cost of that meat some times becomes prohibitive due to the higher labor costs in Japan.