The farmers of the peaceful planet Akir are threatened by the tyrannical warlord Sador (John Saxon), who rules the sinister Malmori Empire. Sador's huge ship carries a weapon called the Stellar Converter, which turns planets into small stars. He threatens to use the Stellar Converter unless the planet submits to him when he returns in several days. Zed (Jeff Corey), the last of the famous Akira Corsairs, is elderly and nearly blind. He suggests that they hire mercenaries to protect the planet. Lacking valuable resources, they can only offer food and shelter in payment. Unable to go himself, Zed offers his ship, which has an artificial intelligence navigation and tactical computer named Nell, for the job if they can find a pilot. The ship is fast and well-armed but cannot defeat Sador alone. Shad (Richard Thomas), a young man who has piloted the ship and is well known to Nell, volunteers for the recruiting mission.Shad's first stop is the Hephaestus space station, which repairs androids. Expecting to find weapons, Shad instead finds only two humans among the androids: Doctor Hephaestus (Sam Jaffe), whose life support has turned him into a cyborg, and his beautiful daughter Nanelia (Darlanne Fluegel). The doctor attempts to force Shad to mate with his daughter. Shad doesn't want to abandon his people, and escapes, with Nanelia following in her own ship. Although she has no weapons, her highly advanced computer systems might be useful. The two separate to look for more mercenaries. Shad comes across Space Cowboy (George Peppard), a spacegoing truck driver from Earth who is ambushed by Space Jackers while delivering a shipment of laser guns to the planet Umateal. Shad fights off the Jackers, thus saving Cowboy's life twice over; they arrive at Umateal just before they watch Sador destroy the planet with his weapon. Lacking the fuel to carry the weapons back home, Cowboy offers to deliver them to Akir. Shad talks Cowboy into sharing his gunslinging experience with the Akira.Later, Shad meets a set of five alien clones who share a group consciousness named Nestor. They admit their life is incredibly dull, since their whole race shares one mind. In order to be entertained, they have sent five members to join Shad's cause. Nestor does not require payment, saying they are completely self-sufficient. Next, Shad recruits Gelt (Robert Vaughn), a wealthy assassin who is so well known he cannot show his face on any civilized planet. Gelt offers his services in trade for the ability to live peacefully hiding among the Akira. Gelt's ship is highly maneuverable and well armed. On his way back to Akir, Shad is approached by Saint-Exmin (Sybil Danning), of the Valkyrie warriors. She is a headstrong woman looking to prove herself in battle. She pilots a small, but extremely fast ship with enhanced firepower. Shad finds her annoying and wishes she would go away, but she tags along.While waiting for Shad's return, Nanelia is captured by a reptilian slaver named Cayman. Cayman possesses a powerful ship with an eclectic crew of aliens. She quickly recruits Cayman to their cause when he learns that they are looking for mercenaries to fight against Sador. The only payment Cayman wants is Sador's head, since Sador's forces had destroyed Cayman's homeworld years ago. The fleet of seven ships return to Akir. Upon reaching the planet's surface, the heroes are greeted with caution by the natives, who are not used to violent species. Eventually, Sador returns, but his armada of attack fighters is intercepted by Shad and his hired warriors. In the opening battle, Gelt skillfully destroys several of Sador's ships but is mortally wounded when his ship crashes. Meanwhile, Cowboy and the Akiran natives, armed with his laser guns, fight off Sador's invading ground forces.Sador survives an assassination attempt by one of the captured Nestors and launches all of his ships in retaliation against the planet. The Akira ground troops, lead by Cowboy, defeat Sador's army, but Zed is killed in the fighting. There is another huge space battle and the mercenaries' ships are destroyed one by one. However, the mercenaries are successful in destroying all of Sador's star fighters and the Stellar Converter, leaving only Sador's flagship. Piloting Nell, Shad and Nanelia are captured by the flagship in a tractor beam. The pair escape in a lifepod after Shad orders Nell to activate the ship's self-destruct program. Sador's flagship is destroyed in the explosion. As Shad and Nanelia return to Akir, Nanelia despairs over the deaths of their friends. Shad tells her that the Akira believe that no one is truly dead when they have been dearly loved and remembered by the living. The Akira will remember the sacrifices made by the mercenaries and honor them forever.