Rex: A Dinosaur’s Story

In Tokachi, Hokkaido, Chie yearns to reunite with her mother Naomi Ito, who has moved to New York. Akira, her paleontologist father, and Daisuke study strange finds from a cave, including a figurine of a child riding a Tyrannosaurus, fossilized and non-fossilized eggs, and ancient writing. The discoveries hint at the lost Mu civilization and set the stage for the journey ahead.

The next day, Akira, Chie, Daisuke, and TV cameraman Fukutomi venture into the cave. They meet Shinoda, an elderly Ainu man who prays to the cave god and guides them deeper inside. There, they find a golden dinosaur idol, a translucent square-pyramid egg, and a crystal-skull column, all pointing to Mu origins.

When Akira and Daisuke touch the egg, the cave begins to collapse. Shinoda stays behind to calm the god of the cave, allowing the others to escape with the egg and an ocarina he gives to Chie. They flee to the surface, shaken but alive.

Back at Akira's home laboratory, Fukutomi informs them that Naomi has been invited to assist with the egg's hatch. Naomi arrives with professional detachment, having focused on her career at the expense of Chie. The family tension heightens as Chie resents Naomi’s absence.

Naomi transfers the nucleus from the dinosaur egg into a sea turtle egg, but the embryo's vitals collapse. Chie plays the ocarina given by Shinoda, reviving the embryo and enabling the infant T. rex to hatch. The creature is soon named Rex and begins life among humans.

Rex makes a TV debut and becomes a national sensation as Chie teaches him basics and even words. Daisuke leverages the publicity to arrange multiple TV commercials for the child-friendly dinosaur. The family watches as Rex’s fame grows, testing their limits and values.

As Rex grows, he is stressed by constant work and public demands. The trio decides to break the contractual obligations to protect him from exploitation. The controversy exposes tensions within the family as they balance care with the media machine surrounding Rex.

On Christmas Eve, Akira is instructed to hand Rex over to the director of a soon-to-be-built dinosaur museum. The family wrestles with the lure of fame versus Rex’s welfare, leading to difficult choices about his future. The emotional stakes center on whether a dinosaur can belong to a family or to a public spectacle.

Chie and Rex flee through town, pursued by the museum director and his associates who ride snowmobiles. With the help of a schoolboy, they evade capture and find temporary shelter in an igloo. Shinoda arrives with Naomi and Akira, reuniting the group to continue their search for a safer path for Rex.

The group returns to the cave and discovers the remains of a Mu temple. In the distance, Rex’s mother appears as a Brocken spectre, signifying a possible reunion with his natural lineage. The moment ties Rex’s fate to Mu’s mythic past.

Chie and Rex share a poignant farewell as Rex walks toward his mother to complete the creature’s natural family bond. The separation marks the end of their direct relationship, yet the hope for a future reunion remains. The group accepts the Mu mystery as part of their lives.

In a post-credits moment, Naomi initially returns to New York but later decides to stay with Chie, Akira, Sanae, and Fukutomi. The family grows closer as they navigate Naomi’s return. A Rex-shaped cloud in the sky hints at Rex’s ongoing bond with his human family.