Reideen

Saiga is an ordinary high school student with a knack for mathematics, leading a peaceful life until a shocking revelation disrupts his routine. The discovery of his archaeologist father's remains, missing for years after an expedition near a peculiar triangular mountain in Japan—often referred to as "Japan's pyramid"—pulls him into a world of mystery. Alongside his father's artifacts and notes, the family faces the unsettling implications of his father's research into this enigmatic site.

Things take a dramatic turn when a meteor crashes nearby, unleashing a powerful robotic entity that wreaks havoc. In the chaos, Saiga finds himself in possession of an ancient bracelet linked to his father's studies, which activates and merges him with a legendary robot buried deep within the pyramid—Reideen. With the alien threat looming larger, Saiga must embrace his newfound bond with Reideen and rise to the challenge of defending humanity against this formidable invader.