Two Ultra Guard scientists, Doctors Segawa and Maeno create a new devastating weapon -- the anti-planet device they christen the R-1. Even in its infancy, the R-1 is said to have the power of 8,000 Hydrogen bombs. With plans to build an even more deadly R-2 device, it is decided a test of the weapons capabilities will be done on the supposedly uninhabited Gieron star, a minor planet in some faraway galaxy. The test proves successful, but a giant flying creature doesn't take too kindly to its home being destroyed. Making its way to Earth, the monster attacks cities and emits radioactive ash. Ultraseven engages the beast in battle.
