The rising sun flag (below) is not the same as the sun disc flag (hinomaru). It was used by the Japanese Navy and Army during Japan's invasion and occupation of Asia between 1895 and 1945, and is still used as the official naval flag of Japan (including the SDF). It is one of the most powerful symbol of the 20-30 million deaths that Japan caused around Asia during this period. In other words it is the equivalent of the Nazi swasitka flag. However, it would be unthinkable for Germany to use the Nazi flag nowadays, even as a naval ensign.

Here is an explanation from Wikipedia's article on Japanese nationalism :

Kyokujitsu-ki(the sun-with rays-flag) or "Japanese war banner". It was the ensign of the Imperial Japanese Navy; and also, one of best-known Japanese nationalist symbols from the First Chinese-Japanese War (1894-95) to the Pacific War (1941-45). This flag was sometimes also used by the Imperial Japanese Army on land, and is now employed by Japanese right-nationalist groups as well as the Japan Maritime Self-Defense Forces.

Should Japan continue to use the Rising Sun flag without fearing to cause anger in other Asian countries ? Would a modern, civilised and humanitarian country use a flag that reminds of its own atrocities during WWII ?