In "Space Adventure Cobra," Johnson, a solitary office worker, longs for an exciting life full of adventure. One day, he experiences a vivid hallucination that brings back memories of Cobra, a renowned space pirate. Armed with the Psychogun on his left arm, Cobra once terrorized the galaxy with his partner, Lady Armaroid, earning both fear and hostility from law enforcement and the Pirate Guild alike.
On Earth, a chance encounter at a casino changes Johnson's fate. His luck draws the attention of Vaiken, the casino's manager and leader of the Pirate Guild, who recognizes him as the disguised Cobra from his dreams. Attempting to seek revenge, Vaiken inadvertently activates the Psychogun hidden beneath Johnson's arm, which awakens his dormant memories and alerts Lady Armaroid.
With his memories restored and having defeated Vaiken once more, Cobra reemerges to thwart the Pirate Guild's criminal activities. Alongside Lady Armaroid, he embarks on a series of galactic adventures, aiding those victimized by the Guild's members.