A monster that was suddenly transfigured by the radioactive explosion of the Superweapon R1 that was launched at Planet Gyeron as a test by the Terrestrial Defense Force. Star Bem Gyeron possesses astonishing regenerative abilities and emits a radioactive gas from its mouth.

It flew into space from the now dead-planet Gyeron and destroyed the Space Observation Ship No. 8. It was completely unfazed by a direct collision with an asteroid and by missile attacks from the Ultra Hawk No. 1 that came to investigate, and made a beeline for Earth.

The Ultra Hawk No 3 was there when it arrived and the Ultra Guard’s new type of bomb blew it to pieces, but by the next day the monster had completely regenerated. The Ultra Guard’s attacks did nothing to stop it, and it approached Tokyo while spewing radioactive ashes into the air.

When Ultraseven arrived to fight it, it reflected his Eye Slugger and damaged Ultraseven using energy ring beams emitted from its hand. The battle came to a close when Ultraseven used his Eye Slugger like a knife to sever its neck.