A dead father's mystery pulls you into something that was always watching you. The first ten episodes move like archaeology, patient, methodical, building layers you won't understand until they collapse. Once it stops pretending to be a high school show, Reideen becomes about a kid learning that the entire universe has been waiting for him to exist, and the animation shifts to match that weight, 3D and 2D moving together like something ancient waking up. This is mecha that earns its slowness.
Saiga lives an ordinary life as a high school student with a talent for mathematics until his father, an archaeologist missing for years, is found dead near a triangular mountain in Japan that some suspect is a man-made pyramid. The discovery sets off a chain of impossible events. A meteor crashes to Earth, unleashing a mechanical entity that ravages everything in its path. With Saiga in danger, a mysterious bracelet tied to his father's research activates and merges him with Reideen, an ancient robot buried within the pyramid. Now Saiga must fight this unknown threat from the sky, balancing school by day with battles by night. Whether the power he has gained brings him glory or fear remains an open question.
