Lucca explains that the device does not itself allow the party to time-travel. Instead, the Gate Key stabilizes pre-existing temporal anomalies, creating the temporary passages that the party uses to cross from one era to the next. The exact manner that Lucca achieves this technological wonder is never clearly explained; however, it is possible that Lucca's work on the Telepod gave her insight into the science of dimensional and temporal teleportation. The Gate Key is arguably the most powerful of Lucca's inventions.During the events in Prehistory surrounding the party's search for the Dreamstone, the Gate Key is lost, leaving the party stranded until it is recovered. After the great feast which won Crono the rare red mineral, Kino, mate of Ayla, stole the device while the party slept. Hunting him down, they discover him in the Forest Maze, moping. It is learned that Kino stole the device out of jealousy for the attention his mate showed Crono, but the device was stolen from him by the Reptites.
It is found in the possession of the Repitie Queen, Azala. She does not believe that it could have been created by any of the 'primitive' humans and believes its power will give her an upper hand in her battle against mankind. After the defeat of Nizbel, Azala's champion, she angrily returns the Gate Key, vowing revenge on Crono and his allies.