After Godzilla's decisive clash with Ghidorah in 1992, the United Nations forms the United Nations Godzilla Countermeasures Center (UNGCC) to curb the threat posed by the monster. Godzilla, Kenpachirō Satsuma in the role of Gojira, becomes the focal point of a bold new plan: salvage Ghidorah's remains and reverse engineer them into two anti-Godzilla weapons—an agile aerial gunship named Garuda and a towering mech modeled after Godzilla itself, Mechagodzilla.
Two years later, and one year after Godzilla’s tumultuous encounter with Mothra and Battra in Yokohama, a Japanese reconnaissance team on Adonoa Island in the Bering Sea uncovers what they believe to be a giant Pteranodon egg. The egg emits a powerful telepathic signal that lures Godzilla back to the area, along with Rodan, an adult Pteranodon irradiated by nuclear waste. Godzilla badly wounds Rodan during the ensuing clash, and the team secures the egg to transport it to a Kyoto research facility. There, the egg somehow imprints on Azusa Gojo, a young scientist, Azusa Gojo, Ryoko Sano.
A juvenile Godzillasaurus soon hatches from the egg. The scientists nickname the creature Baby Godzilla, and the little one answers to the psychic call that keeps pulling the two giants toward Kyoto. The JSDF responds by deploying Mechagodzilla, a weapon built around the earlier Ghidorah tech to intercept Godzilla as he heads toward Kyoto. The battle begins with Mechagodzilla enjoying the upper hand, but Godzilla breaks through with an energy pulse, turning the fight back in his favor as he searches for Baby.
As scientists study the telepathic link between Baby and Godzilla, they reveal a startling detail: Baby possesses a second brain in its hips that controls movement. The UNGCC suspects that Godzilla’s species may share this trait and devises a plan to lure him into another confrontation by using Baby as bait. The plan introduces a new tool, the G-Crusher, installed into Mechagodzilla, meant to penetrate Godzilla’s hide and destroy that second brain. Miki Saegusa, Megumi Odaka, is drafted to join Mechagodzilla’s crew to locate Godzilla’s second brain, despite her initial trepidation over her mental link to the creature.
The scheme is complicated when Rodan—now transformed into Fire Rodan—responds to Baby’s call and seizes control of the UNGCC transport, forcing a dangerous reversal of plans. Garuda, piloted by Kazuma Aoki, Masahiro Takashima, and Mechagodzilla push forward, and a new, upgraded Garuda-Mechagodzilla fusion—Super-Mechagodzilla—emerges to pursue Rodan. Mechagodzilla temporarily paralyzes Godzilla, but Rodan sacrifices himself, transferring his power to regenerate Godzilla’s second brain. Empowered, Godzilla surges back, overpowers Super-Mechagodzilla, and shatters the alien machine.
With the obstacle cleared, Godzilla finds Baby and, reassured by Miki’s telepathic encouragement, gently coaxes the youngster to accompany him into the ocean. The two giants retreat together, leaving Kyoto to recover from the devastated, yet triumphant, night of battle.
