Eioneus is a planet in the Metalion Solar System. It is a planet with grasses, trees, rocks and volcanoes.
Most of the time the Bacterians attacked Eioneus and transformed it into a base, only to be liberated by Vic Viper later. In Gradius Gaiden, Eioneus was damaged by a black hole. However, in Gradius Galaxies, Eioneus was not worse for weary and a civilization seems to have formed.