8 Eyes is set in a post-apocalyptic future. Mankind is recovering from hundreds of years of chaos and nuclear war, and civilization is being rebuilt by the Great King, who harnesses the power of eight jewels. The jewels, known as the 8 Eyes, were formed at the centers of eight nuclear explosions that came close to destroying the Earth. The 8 Eyes have mysterious power which, in the wrong hands, could bring about the end of the world. The Great King's eight power-hungry dukes steal the jewels for themselves and banish the King to the nuclear wastelands, threatening to once again plunge the Earth into war.

The player controls Orin the Falconer and his fighting falcon Cutrus. His mission is to infiltrate the Dukes' eight castles and retrieve the 8 Eyes. With the help of Cutrus, you must fight the Dukes' soldiers, nuclear mutants, and the duke of each castle to retrieve the jewels. After the jewels have been recovered, you must return them to the Altar of Peace so that the Great King may return and finish rebuilding the Earth.