Kumamoto city is located in Japan's second most-populous island

Kumamoto - where the collapsed Aeon Mall is located - is a city on the Kyushu island of Japan. Japan doesn't have a mainland. It is made up of four primary islands, one of which is Kyushu. The other three are Honshu, Hokkaido and Shikoku. There are also thousands of smaller islands that sit further out. The southern island of Kyushu is the third-largest of the four main islands in Japan, and the second most populous.