Radiation Island takes place in the middle of WWII, where the Japanese Imperial Army, and the American Armed forces are battling in the Pacific Ocean for control over various islands. To get the upper hand in the battle, the Imperial army enlisted you as well as other scientists/Physicists to develop a new and powerful weapon, Teleportation. As the tests are conducted, various events begin to happen, such as Villagers vanishing, various people becoming violent and aggressive, and radiation popping up around the Islands. It was also known that the United States were trying to develop teleportation for themselves as well, and a testing ship was also spotted of the coast of the Island. The Final Test ( or the beginning of the game ) had been enacted, and thats when all hell broke loose. People turned into mindless monstrosities, animals suddenly multiplying, and you teleporting everywhere else. After the Final Test, you appear on the bottom island's coast, with nothing but your bare hands and a Journal. This is when the game begins, and the Protaganist begins his adventure to solve the mystery of the island as well as get off of it.
Most of the story can be found i♙ Journal Entries in-game.
The story of Radiation is set 11 years before you are abandoned there because of the Philadelphia experiment.