Somewhere in space a battle is going on. Mechanized knights of unknown origin battle each other, ending up on the Moon, where a fight to the death takes place. Apparently Orgun has been marked for death by his own kind, the Evoluders, a bloodthirsty race of machine-cyborgs bent on conquering and destruction. Meanwhile back on Earth in City No. 5, a college student named Tomoru Shindo is somehow contacted by Orgun as he is dying on the Moon. Orgun has also been sending instructions to Earth received by the Earth Defense Force, for building a new Orgun, one which Tomoru is now destined to meet.

Detonator Orgun is a cyberpunk/sci-fi adventure game based on the anime of the same title that takes place far in the future within the Solar system. Tomoru Shindo is the main character of this game. Gameplay consists of clicking on decisions from a menu, such as Look, Think, Talk, Move, etc. The original voice actors from the anime also do the voice acting in this game.