ThrowawayTestr parent
Either you have a multicultural society or you have a high trust society, you can't have both. Why? Because people have an instinctual distrust of people dissimilar to them.
Japan is not a high trust society. Japanese people are highly suspicious of other people, including Japanese. Japanese people are extremely concerned about how they are viewed and judged by others; the conformity is a desire to be accepted in society, and such trust and acceptance is not freely given but instead quickly taken away. Among my friends from Japan who have left the country, this is by far the most oppressive social more that they feel compelled to follow. And among those who have moved to Japan, many feel that learning the social rules and earning that trust was a significant accomplishment, and a handful want to preserve that exclusion because of how much effort it took to make themselves part of society.
Japanese social groups are extremely exclusive- on the broadest level, foreigners are excluded from some establishments, banking and housing services are sometimes inaccessible to foreigners. And on a smaller level, there are also establishments that do not accept new customers without an introduction, local or not. Such exclusions are an integral part of the culture - the language itself is a shibboleth, you know your place and standing in the world by the language other people use when they speak to you.