第1話: ジャンキ・サイガは父親の遺体が発見された後、金のブレスレットと巨大ロボットを発見する。

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"I used to think that stories of ordinary high school students riding in gigantic robots and fighting with monsters belonged to the realm of those old anime shows. Sure, it couldn't happen in the real world. But then, why is it happening to me now?!" Japan, in the near future. Junki Saiga is a typical high school student who lives with his mother and his little sister Kuraka. One day, the police call and inform that the remains of Junki's father, an archaeologist disappeared ten years before, were found at Kurokami (Black God) Mountain, a bizarre pyramid-shaped peak in Iwate Prefecture. The whole family heads to the site. But Junki becomes unconscious in the archaeological site and sees a strange illusion. When he wakes up, he's holding a golden bracelet in his hand, with ancient inscriptions which read, "The Great Reideen." That night, a meteorite falls onto the earth and a huge mechanical monster appears from the artificial lake at the nearby dam. And as if to respond to the phenomenon, a gigantic figure shining in gold manifests itself on the Kurokami Mountain. Junki has accidentally obtained a titanic force. Would it bring him glory, or terror? (Source: Production IG)