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Momotaro, the human leader of an animal navy fleet, has given his animal vassals a mission to bomb Pearl Harbor (also referred to as Demon Island). The Canine, Monkey, & Pheasant units all volunteered to accomplish the mission in the honor of their own country.
Three years have passed since little Gen and his mother lost their family to "Pika", the bomb dropped on Hiroshima. They and everyone around them are trying their best to survive and find a place in the new world, which is not easy given the scale of destruction and the fact that people are still dying from the post-effects of exposure to radiation. Gen finds new friends among the homeless kids who treasure their freedom and tries hard to help his mother and live by his father's principles.