In 2013, human cities come under attack by the Kaijus: colossal beasts who come through an interdimensional portal on the Pacific Ocean floor. To combat them, the Pacific Rim nations build the Jaegers: equally colossal humanoid war machines. Each Jaeger is piloted by two people whose brains are linked to share the overwhelming mental load of operating the machine. The Jaegers are initially effective, but many are destroyed as the Kaijus grow more powerful and their attacks more frequent. In 2025, the involved governments deem the Jaeger program unviable, and discontinue it in favor of building massive coastal walls to protect humanity from the Kaijus. The four remaining Jaegers are redeployed to Hong Kong to defend the coast until the wall's completion. Jaeger commander Stacker Pentecost (Elba) devises a plan to end the war by destroying the portal with a thermonuclear bomb.
Pentecost approaches retired pilot Raleigh Becket (Hunnam) and convinces him to return and pilot Gipsy Danger, the Jaeger he and his brother Yancy once piloted. During a mission off the coast of Alaska in 2020, Yancy was killed by a Kaiju while connected to his brother, traumatizing Raleigh. In Hong Kong, Raleigh is antagonized by Chuck Hansen (Kazinsky), co-pilot of the Jaeger Striker Eureka, who sees Raleigh as unreliable. Later, Raleigh tests with potential co-pilots to find one with whom he connects strongly, which ensures effective performance in battle. Sensing a strong connection, Raleigh demands to be partnered with Mako Mori (Kikuchi), the director of the Jaeger refurbishment project. Pentecost opposes, Mako being his adoptive daughter, but he eventually relents. During the duo's initial test run, Mako becomes engrossed in a childhood memory of the Kaiju attack which orphaned her, and nearly discharges Gipsy Danger's weapons in the hangar; Pentecost deems her unready for combat. Later, the other Jaegers are tasked with fending off a double Kaiju attack in Hong