Japan, officially known as the Empire of Japan, was an island country in northeastern Asia. Its capital city was Tokyo.
Sometime before the 2012 Apocalypse, Tony Delgatto's son Wil moved to Japan and started a family. Later, as the apocalypse ran its course, Tony called his family, but an earthquake disrupted the telephone connection. It's assumed that his family was killed after their house was destroyed.
It was reported on the BBC which is watched by Genesis' crew, Tony and Harry in the Genesis ship discovered that Tokyo was hit by a massive earthquake and much of the country was flooded by tsunamis.
In the aftermath of the 2012 Apocalypse, Japan was destroyed and rendered uninhabitable with most of its population being killed. The only known survivor of Japan is its Prime Minister.