There are many possible explanations for Hiroshima’s success. Several are outlined below.
Occupation policy of the GHQ
The US-led General Headquarters (GHQ) basically ruled Japan, while keeping its prewar system of central and local administrations as well as police organizations, aside from leaders accused of war crimes. This helped maintain public order, even after the surrender of Japan. No civil war or revolution took place.

New identity
During the prewar and wartime periods in Japan, the nation’s sovereign power resided with the Emperor. Then, the country began to take on a militaristic tinge after the outbreak of the First Sino-Japanese war. However, after the World War II, most citizens accepted the reformed national structure as a peaceful state under the new Constitution. A pacifist principle of “never waging war again” became a backbone for a new identity for the people of Japan and enabled the country to concentrate on production activities.
As in other Japanese cities, the people of Hiroshima accepted this shift in their identity from a wartime “military capital” to a postwar “city of peace,” allowing them to concentrate on reconstruction efforts.

Reconstruction measures led by national and local governments
War damage reconstruction was a challenge of national significance in Japan. In 1945, the War Damage Reconstruction Agency was established and launched reconstruction measures as a national policy. In addition, thanks to the enactment of the Hiroshima Peace Memorial City Construction Law (a special law that applied to a specific local entity―based on Article 95 of the Japanese Constitution), Hiroshima received generous support from the national government to accelerate its reconstruction.

Continuation of social structures
After the Meiji Restoration in 1868, politically, legally, economically, culturally, and educationally Japan promoted the modernization of its social structures to catch up with the Western world. Most of this social system (particularly the Civil Code and administrative systems) has been kept after World War II, even though the state as a whole was temporarily impoverished due to the defeat in war and was reformed by the GHQ to a certain extent. In this regard, Japan was able to effectively achieve reconstruction using its already-established social systems, though it had much more post conflict rebuilding to do than many other countries in the modern age, as those countries had to begin its nation-building from scratch.

Industrial structure in Hiroshima and a working population
Before the atomic bombing, Hiroshima City had a relatively high concentration of manufacturing for the size of its population. The atomic bombing caused enormous in damage to factories/offices as well as loss in the number of workers. Meanwhile, factors including below contributed to the recovery and reconstruction of Hiroshima Prefecture’s manufacturing industry, many of the major factories survived with relatively minor damage to their facilities due to being located away from the hypocenter, The ratio of the number of manufacturing workers out of the total number of employees in the prefecture was higher than the pre and postwar national averages, a steady supply of workers including female workers, a relatively smooth transfer of military facilities to private company ownership, especially in the manufacturing industry, and boom during the special procurement that came with the Korean war.