Japan is an island country located in East Asia. Although it has had twenty-one S-Rank Hunters in its history, including the famed Goto Ryuji, seven of them were killed in the 4th Jeju Island Raid, drastically diminishing the country's military power and leaving the country almost completely defenseless when a S-Rank Gate suddenly spawned in Tokyo several months later.
As a result, the raid was a complete disaster, causing the deaths of millions (including three S-Ranks), and would have resulted in an international crisis had it not been for Sung Jinwoo, who arrived in Japan several days after the dungeon break occurred and easily cleared the gate all on his own within a week. Shortly afterwards, Matsumoto Shigeo, the Chairman of the Japanese Hunters Association, gave himself up to the Japanese authorities for his responsibility in causing the disaster.