Terror of Mechagodzilla (Movie)
Following the events of Godzilla vs. Mechagodzilla, Interpol agents search for Mechagodzilla's remains at the bottom of the Okinawan Sea in the hopes of gathering information on the robot's builders, the alien Simeons. However, their submarine is attacked by a giant, aquatic dinosaur called Titanosaurus and the crew vanishes.
Interpol launches an investigation into the incident. With the help of marine biologist Akira Ichinose, they trace Titanosaurus to a reclusive, mad scientist named Shinzô Mafune, who wants to destroy mankind. While the group is visiting the scientist's old home, they meet Mafune's daughter, Katsura, who claims her father is dead and that she burned his notes about Titanosaurus at his request. Unbeknownst to Interpol, the living Mafune is visited by Tsuda, an aide to the Simeon leader Mugal, who is leading a project to rebuild Mechagodzilla. Mugal offers the Simeons' services to Mafune so that their respective monsters can wipe out mankind and allow them to rebuild the world for themselves.
Complicating matters, Ichinose falls in love with Katsura and unwittingly gives her Interpol's information on the Simeons, Mechagodzilla, and Titanosaurus. She is also revealed to be a cyborg, having undergone cybernetic surgery after she was nearly killed during one of her father's experiments as a child, and implanted with Mechagodzilla's control device. Additionally, an inpatient Mafune releases Titanosaurus on Yokosuka without the aliens' permission. While Interpol discovers the dinosaur is vulnerable to supersonic waves, Katsura destroys their supersonic wave oscillator. However, Godzilla arrives and easily defeats Titanosaurus, causing the latter to retreat.
When Ichinose visits Katsura, the Simeons capture him and force him to watch as they unleash Mechagodzilla 2 and Titanosaurus on Tokyo while Interpol struggles to repair their wave oscillator and the Japanese armed forces struggle to fend off the monsters. Godzilla arrives but is initially outmatched until Interpol distracts Titanosaurus with the repaired wave oscillator, allowing Godzilla to focus on Mechagodzilla 2. Interpol agents infiltrate the aliens' hideout, rescue Ichinose, and kill Mafune and many of the aliens. The remaining Simeons attempt to escape, but Godzilla shoots down their ships with its atomic breath. The wounded Katsura shoots herself to destroy Mechagodzilla 2's control device and dies in Ichinose's arms. With the robot non-functional, Godzilla tosses it into a chasm before blasting it with its atomic breath, causing it to explode and get buried. With help from Interpol, Godzilla then defeats Titanosaurus, who returns to the sea.