From a young age, she lived on Solgell Island with her father, who died seven years before the film began. When the researchers arrive on the island, she hides from them, making them believe that the island is uninhabited. She is later discovered by Goro Maki, but she flees underwater, leading him to believe she was a mirage. She forms a friendship with the premature Godzilla baby Minilla, and can attract him by calling him. She is later discovered by the team when she steals clothes off the line at the scientists' camp. Maki tracks her down and enters her cave, but slips and falls unconscious until Saeko returns.
She at first mistakes Goro for a thief seeking to steal her father's notebook, but later realizes he had just come for his shirt, which he then gives to her. After the scientists' camp is destroyed, she allows them to be sheltered in her cave. Shortly after, the men fall victim to a virus, for which Saeko knows the cure. She and Goro seek it, and nearly wake Kumonga in the process. Shortly after the cure is administered and the men have recovered, she is attacked by a Kamacuras. She calls to Minilla, and he in turn summons Godzilla. Goro Maki then gets her to safety, only for the pair to be attacked by Kumonga.
She and Goro escape back to the cave where the scientists have decided to leave the island. She and Goro are then sent to put up a radio antenna on top of the cave so that they could call for help. She, Goro, and the scientists are later picked up by a United Nations submarine, while Godzilla and Minilla go into hibernation together after defeating Kumonga while the island freezes over.
- Saeko's name is changed to Reiko (or sometimes "Riko") in international releases of Son of Godzilla.