It appears that because of the lack of stringent laws in place in the country of Japan, the flotsam and jetsam of the world seek a new start there. The real question should be can the United Nations force the Japanese government into denying any type of refugee. Should this be a map for future refugees?
There is an inherent risk with allowing others into your country. The number of refugees across the globe is on the rise. Most of these people have good intentions and would likely make good citizens of their new home. The problem is that with inviting so many people in, a country invites a lot of risk. We will see a rise in attacks if we continue with current refugee laws.
Far too often other countries like to meddle in the affairs of others, pontificating and trying to dictate what is appropriate. Japan's laws only need be as tough as its citizens and government think. No one else has any standing or right to dictate the terms and conditions of refugee, or other, status of another country.
In comparison with the huge number of refugees and migrants seeking refuge across continental Europe, Japan is noteworthy for the relatively few migrants that they have allowed to cross their borders. There will always be outlying situations where the law needs to be closely examined but these outliers should not prompt tougher laws unilaterally.