Gimsa is the newborn son of Queen Lilia and King Astralta III (formerly Prince Ithaca) of the planet Astria in the Andromeda Galaxy. His birth coincides with an invasion by sentient machines that transform Astria into a mechanical wasteland and assimilate the king and his ministers. Fleeing with his mother into the desert, Gimsa becomes separated from his twin sister Affle during their escape.

He comes of age under the protection of High Priest Kufu, a refugee from Murat, within a guerrilla resistance movement fighting the machine occupation. This group includes the robots Arc and Beta, who guide the refugees. During his upbringing, Gimsa develops a unique energy beam ability, a power crucial to the resistance's strategy.

As a teenager, Gimsa reunites with his sister Affle and mother Lilia. Queen Lilia later surrenders to the machines, embracing a state of emotionless bliss and urging her children to join her before accepting her impending demise during Astria's destruction.

A significant revelation occurs when Kufu discloses that Murat refugees secretly manipulated Astrian society for generations, selectively breeding the royal bloodlines to produce individuals with enhanced capabilities. Gimsa and Affle are the culmination of this project. Their energy beam powers, ineffective individually, become exponentially stronger when combined, though this proves insufficient to halt the machine threat.

Gimsa and Affle form a romantic relationship before learning they are twins. Despite the revelation of their kinship, they choose to remain together, rationalizing incest as historically accepted within royal lineages. Ultimately, Kufu sacrifices himself to destroy Astria and the machines entirely. Gimsa and Affle escape in a capsule, crash-landing and perishing on a primitive planet. Their cells then seed life on the barren world through panspermia, potentially reincarnating over eons to become humanity's progenitors.