Taking place after Darius II, Proco and Tiat realized just how far Belser had reached into space and hurried back to Orga in hopes of warning the populace. The time they were gone was just enough time for Belser's allies to regroup and spread beyond Darius and begin their invasion of Orga. Once again, Proco and Tiat are quick to throw themselves into battle.
Though similar to the original Darius series, Darius Twin featured slightly different gameplay features, most notably in the player's power-ups. Players collected weapon and shield power-ups from square shaped enemies that approached the player from the front and behind, but once players died after collecting a certain amount of power-ups, the power-ups the player collected stayed with the ship post-destruction. Also, players 1 and 2 were allowed their own separate amounts of lives (Taito horizontal shooter motif), but there were no continues in the game.
Darius Twin adopts from Darius II the idea of the Captains, mid bosses that adopts, like bosses, aquatic life forms. Like Darius II, the captains for this game are well known bosses from earlier Darius games. The captains for this game are:
Little Stripes (angelfish)
Guard Savage (tiger shark)
My Home Daddy (hermit crab)
Burst Out (pufferfish)
On the last stage of the game, the only enemies that are placed before the bosses are captains.