A messenger from the Andromeda Galaxy, thirty thousand light-years away, arrives on Earth to protect humanity from otherworldly invaders. Disguised as the scientist Ryusaku Hata, he raises five orphan children—Yukio, Tomohiro, Kurazo, Goro, and Kyoko—who help investigate strange phenomena and, when danger strikes, call for their guardian using a magic radio transmitter. When the signal is sent, Hata transforms into National Kid, a caped hero with superhuman strength, the power to fly with arms outstretched, and an Eroruya ray gun that fires dazzling beams.

The first threat comes from the Incas, an alien race from Venus who deem humanity too reckless with nuclear weapons. They unleash flying saucers on Tokyo, spread a devastating virus, and worship a deity called Awika. National Kid seeks rare minerals in the mountains to create a cure and battles the Inca commander Aura and her lieutenants Vemana and Kabia. After that, the undersea people known as the Coelacanth emerge from the ocean depths, led by the demonic Nelkon. These ancient fish‑men ride a monstrous submarine called Guilton and wage war on the surface, forcing National Kid to fight both aboard the vessel and in the sea itself.

The underground people then surface, desperate for energy after their solar reserves run low. Their president, Helnstein, seeks the formula for a powerful rare element called Cobalcium and launches UFO attacks on Japan. National Kid must prevent them from stealing the secret and plunging the world into darkness. In the final story arc, a space boy named Taro crashes to Earth in an egg‑shaped ship and loses his memory. The children befriend him, but Taro’s father, leader of the powerful planet Mirzan, is manipulated by Helnstein into believing Earth is a menace. As a giant monster, Gyabura, is unleashed on the city, National Kid discovers that the beast’s only weakness is its eyes. Taro regains his memory and helps persuade his father to call off the attack, and together they defeat the lingering underground forces and the Zarrocos, a race of thin‑nosed aliens who command Gyabura. After these battles, National Kid reveals his true identity and returns to Andromeda, leaving the children to carry on his legacy of protecting peace.