In 2013, massive alien monsters called Kaiju begin emerging from an interdimensional portal, “the Breach” at the bottom of the Pacific Ocean and attacking coastal cities. In response, humanity builds massive mecha called Jaegers, each co-piloted by two or more people who share a mental link by a process called “Drifting” to share the mental stress of piloting the machine.

In 2020, brothers Yancy and Raleigh Becket pilot the American Jaeger, Gipsy Danger, to defend Anchorage from a Category-3 Kaiju codenamed Knifehead, who severely damages Gipsy, killing Yancy. Raleigh kills Knifehead and pilots Gipsy solo to shore before collapsing. Traumatized by the loss of his brother and the stress of piloting alone, Raleigh quits the Jaeger program.

Five years later, world leaders decide to cease funding for the Jaeger program and replace it with coastal defense walls, since Kaiju attack frequency is increasing and Jaegers are being destroyed faster than they can be built. The walls quickly prove ineffective. The remaining Jaegers are relocated to Hong Kong under the command of Marshal Stacker Pentecost who plans to try to destroy the Breach using a tactical nuclear weapon, despite unsuccessful previous attempts.

Raleigh, now working in wall construction, is recruited by Pentecost for the mission. At the Hong Kong base, the Shatterdome, Raleigh is introduced to Mako Mori, the director of the Jaeger restoration program. Four Jaegers remain operational – the refurbished Gipsy Danger, the Russian Cherno Alpha, the Chinese Crimson Typhoon, and the Australian Striker Eureka piloted by father-and-son team, Herc and Chuck Hansen. To find a new co-pilot, Raleigh participates in tryouts; he decides that he and Mako are “Drift-compatible”. During their first test in Gipsy Danger, Mako falls out of alignment while reliving the memory of an attack on Tokyo by the Kaiju Onibaba, nearly firing Gipsy’s energy cannon and destroying the base. As a result, Pentecost grounds Mako. Raleigh calls out Pentecost on this. Pentecost reveals he adopted Mako after her parents were lost in the Kaiju attack.

Pentecost consults Kaiju experts Newton Geiszler and Hermann Gottlieb. Hermann claims the Breach will stabilize and the Kaiju will increase in number, but this will allow the assault to succeed. Against Pentecost’s recommendation, Newton drifts with a Kaiju’s brain to learn more about them, discovering that Kaiju are bioweapons grown by aliens so they can colonize Earth. Pentecost instructs Newton to find black market dealer Hannibal Chau to obtain another Kaiju brain to drift with. Newton realizes the Kaiju hive mind gained access to his brain, since drifting is a two-way link, and the two newest Kaiju to emerge, Leatherback and Otachi, are sent simultaneously to find him in Hong Kong.

All Jaegers except Gipsy Danger are dispatched to intervene. Otachi destroys Crimson Typhoon, while Leatherback destroys Cherno Alpha and disables Striker Eureka with an EMP blast, injuring Herc. As the only non-digital Jaeger, the nuclear-powered Gipsy Danger is sent by Pentecost to help. Gipsy kills both Leatherback and Otachi. Newton and Hannibal go to harvest Otachi’s secondary brain but discover she is pregnant. The infant Kaiju bursts out and devours Hannibal before choking on its own umbilical cord. Newton and Hermann drift with the infant’s brain, discovering that the Breach only opens in the presence of a Kaiju’s DNA.

Pentecost reveals to Raleigh he is ill from radiation poisoning due to piloting a first-generation Jaeger alone to save a young Mako, and has been unable to pilot a Jaeger since. When two new Kaiju, Scunner and Raiju, are detected guarding the Breach, Gipsy and the repaired Striker, piloted by Pentecost and Chuck, approach the Breach, where a new Category-5 Kaiju, Slattern, appears. When the Jaegers are attacked by the Kaiju, Gipsy kills Raiju, but is crippled. Pentecost and Chuck sacrifice themselves and Striker, killing Scunner, then Gipsy slaughters Slattern, riding its corpse into the Breach. Raleigh ejects Mako from Gipsy, manually triggers Gipsy’s nuclear reactor core’s self-destruct, and ejects himself before it explodes and seals the Breach. Raleigh and Mako’s escape pods surface in the Pacific Ocean; they embrace as rescue helicopters arrive and humanity rejoices at the defeat of the kaiju.

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