Two of the most popular industries to come out of Japan is manga, the equivalent of comic books, and anime, the equivalent of cartoons. These works explore a variety of subjects ranging from super-powered individuals fighting for their friends to immersion into traditional stories. However, they extend beyond the imagination, as they also tackle real-world events. The dropping of the atomic bombs on Hiroshima and Nagasaki acted as direct influences on many creators. One author, Keiji Nakazawa created a manga loosely based off of his experiences as a survivor the bombing of Hiroshima. Barefoot Gen includes what the city went through as the bomb detonated, and it is truly a gruesome depiction that is hardly able to be comprehended. It goes through the very real circumstances of how countless people were not expecting their lives to be cut short, and those who survived had to deal with grief and hopelessness. Other creators make more subtle nods to the bomb and its effects. While the actual dosages of radiation received by the victims are unknown, there were an increased risk of cancer, birth defects, and mental retardation among many children, both born and unborn.[1] Since so many children experienced mutations due to the bombs, this was translated into manga and anime as “radioactive mutations or having some extraordinary powers, in addition to taking on more adult responsibilities at an early age.”[2] Numerous creators also pin the blame of the bombings on the fight for power. Katsuhiro Otomo’s Akira portrays adults and their lust for the alien technology “Akira,” which ultimately consumes Neo-Tokyo.[3] 
The subject of the atomic bomb is taken very seriously in Japan, which is in stark contrast to its portrayal in American cartoons. Nowadays, the mushroom cloud (which is made due to an atom bomb) is used as a comedic device in some cases. The famed Spongebob Squarepants often uses it to exaggerate the destruction caused by a character. I am unsure how Japan sees this use, but I doubt it is seen with the same humor as Americans see it.
[1] http://large.stanford.edu/courses/2013/ph241/yapa2/
[2] https://qz.com/842067/the-apocalyptic-echoes-of-the-atomic-bomb-in-japans-anime-and-manga/
[3] Ibid.