Saiga, a talented math whiz with an unremarkable high school existence, experienced an unexpected upheaval when he received news of his father's remains being discovered. Saiga's father, an esteemed archaeologist, had disappeared some time ago while exploring a pyramid-shaped mountain in Japan colloquially known as "Japan's Pyramid." Curiously, the remains found along with Saiga's father were emblazoned with cryptic messages and curious artifacts. As Saiga and his family readied themselves to identify these objects, a strange meteor crash-landed and unleashed a robotic lifeform that plunged Saiga into mayhem and imperilled his life. He discovered himself joined with an archaic robot known as Reideen, which his father had investigated at the pyramid and named, after a mystical bracelet was activated by the meteor's impact. Equipped with Reideen and his own set of skills, Saiga is tasked with thwarting this unknown extraterrestrial threat, which has descended upon the planet from the heavens.