Mirai Shounen Conan

Conan was the only child born on Remnant Island, a place settled by a group of refugees while they fled a terrifying wave of magnetic bombs that wiped out most of humanity. After 20 years, most of the castaways have died, save for Conan and the wise old man that raised him. Believing Remnant Island to be the last inhabited place on Earth, Conan is shocked when he discovers a young girl named Lana washed up on the beach one day. Though he is thrilled to learn that humanity has survived, Lana tells him the nation of Industria wants her as a hostage to force her grandfather, Dr. Lao, to power their machinery. Their conversation is cut short when Industria's top pilot, Monsley, suddenly appears and seizes Lana. Determined to save her, Conan immediately sets off from Remnant Island and begins a journey that will ultimately determine the fate of the world.