While exploring space in search of knowledge, humanity uncovers three enormous trucks and a massive spacecraft from an extinct alien civilization on the planet Solo. During the excavation, the humanoid Buff Clan, another extraterrestrial race, arrives on Solo. Despite orders forbidding it, Karala Ajiba—daughter of the Buff Clan's military leader—descends to the planet. In pursuit of her, the Buff Clan attacks the Earth settlement, destroying it in an attempt to reclaim Karala. With no other recourse, Earth residents Cosmo Yuuki, Kasha Imhof, and Bes Jordan board the trucks, which combine to form the mighty giant robot known as the Ideon. Using the Ideon, they fight back against their assailants. The surviving humans flee aboard the Solo Ship, relentlessly chased by the Buff Clan, who seek to obtain the Ideon and its mysterious power source.