When Little Mako is in the alleyway, every object on the set was rigged to the same hydraulic system. Whenever the giant monster was to take a step, everything bounced or shook in unison, including the puddles.
According to Travis Beacham, an earlier version of the script would have Mako (Rinko Kikuchi) and Raleigh (Charlie Hunnam) speaking two different languages for the majority of the film. After connecting as pilots, they would slowly begin to understand one another, and before the end would hear each other speaking in their own respective languages. The only remnant of a language barrier between the characters in the film is in the scene where Raleigh talks to Mako in Japanese, surprising her that he knows her home language.
A life-sized version of the robot cockpit was built on a soundstage at Pinewood Studios in Toronto. It weighed about 20 tons, and stood nearly four stories high. It was built on a gigantic hydraulic gimbal, which would move, shake, vibrate, drop, and rock the entire set as if it were actually being piloted. A smaller version was also built with a smaller gimbal, allowing for different movements. The VFX team used some of the Conn-pod footage for reference while animating the robots. The set was also redressed to depict the interior of each robot differently.
Screenwriter Travis Beacham also wrote the graphic novel Pacific Rim: Tales from Year Zero. Released along with the movie, Tales from Year Zero serves as a prologue to the film and is set twelve years before its events.
(at around 1h 25 mins) The inside of the building that Gipsy's fist smashes through was created using miniatures. Many of the components of the office cubicles were made using 3D printers. The lighting was practical, and done to scale. Once the set was ready, a large green mandrel was rammed through it. This was digitally replaced with Gipsy's fist.
Travis Beacham, the screenwriter, got the idea for the movie while walking along the California coastline on a foggy morning. The shape of the pier looked like a creature rising from the water, and he imagined a large robot waiting on the shore to battle it.
The Kaiju's roars comprise layer upon layer of animal roars and growls which were filtered, sped up, and slowed down to create the roar of alien behemoths. Then, to add emotion and a sense of intelligence, supervising sound editor Scott Martin Gershin and director Guillermo del Toro added samples of their own voices.
Visual effects supervisor John Knoll and Guillermo del Toro spent several weeks discussing the physics of the giant characters, and went into very specific detail, such as how the air displacement from a Jaeger moving between skyscrapers would shake the building's windows.
The computer is voiced by Ellen McLain who also voiced GLaDOS, the AI from Portal (2007) and Portal 2 (2011). This is in fact a cameo by GLaDOS, as Guillermo del Toro was such a fan of the games that he approached the game's developers, Valve, who approved. Del Toro said in an interview for the Toronto Sun: ""I wanted very much to have her, because I'm a big Portal fan. But just as a wink. She's not cake-obsessed. She's not out to destroy humanity." He further explained: "Look, there's no A.I. I'd rather have than GlaDOS, but McLain's voice in the movie, due in theaters July 12, has been modulated a bit to be less similar to the distinctive tone of Portal's unforgettable antagonist. The filter we're using is slightly less GLaDOS. Slightly. The one in the trailer I wanted to be full-on GlaDOS." The GLaDOS voice itself is inspired by the computer in The Thirteenth Floor (1999).
In Hungary, the trailers for the movie could not mention the name of the main robot, Gipsy Danger since the name was seen as offensive to gypsy or "roma" people, who form a large ethnic group in the country. In the dub of the movie itself, the name is spoken freely, but it's left in English. This is because it is a reference to a type of airplane engine, not the people in question.
In March 2013, YouTube channel "Dumb Drum" created a "sweded" version of Pacific Rim's trailer. Less than two weeks later, Guillermo del Toro commented on the video at WonderCon 2013, calling it a "masterpiece" and saying that it inspired him to create the second trailer for the film. He also invited the filmmakers to the Hollywood premiere. When the film was released on home video, Legendary Pictures contacted "Dumb Drum" and asked for their help promoting the release. In October 2013, they released several "sweded" versions of scenes from the movie. These new videos were made 15 second intervals for sharing on social media websites.
This was both director Guillermo del Toro and cinematographer Guillermo Navarro's first experience shooting with digital cameras. Navarro bought seven Red Epic cameras specifically for the film and used his own lenses, as he prefers shooting with his own camera equipment over renting it.
Karloff, one of the kaiju from the opening sequence, is named after Boris Karloff. The nickname was given because the creature's head resembles the dessicated face of Karloff's The Mummy (1932) character, Imhotep.
Pacific Rim's Jaegers are a staple of Japanese anime, where they are often referred to as mecha. Similar to many mecha anime series, Jaegers are controlled from within by human pilots, distinguishing them from other depictions of robots as automated, sentient, or externally controlled.
(at around 55 mins) A prominent street sign in Hong Kong identifies the intersection of "Tull Street" and "Fong Street". Thomas Tull is the president of Legendary Pictures (which financed the film), and Henry Fong is one of the film's concept artists.
In the weeks before the film's release, several popular YouTube channels collaborated with the filmmakers to produce a short video titled "Pacific Rim: Training Day." The short even features a brief cameo by Guillermo del Toro. The collaborating channels included Jesse Cox, Press Heart to Continue, Total Biscuit, Husky Starcraft, Game Grumps, Crabcat Industries, and The Game Station.
Guillermo del Toro was inspired by the anime and tokusatsu (special-effects TV series and films) of his youth. He specifically cites Tetsujin nijûhachi-go (1963) as a major influence. Despite this, he wanted to avoid referencing other works of fiction in the design of the robots and monsters.
(at around 1h 25 mins) When the Gipsy Danger is fighting the second Kaiju in Hong Kong, it punches through a building and sets off a set of Newton's Balls or Newton's Cradle. The scientist that the Kaiju was chasing is named Dr. Newton Geizler.
Ron Perlman's character, Hannibal Chau, could be named after James Hong's character, Hannibal Chew, in Bladerunner, as Guillermo del Toro has named the film as a huge inspiration for him as a director.
The movie is dedicated to the memory of "monster masters" Ray Harryhausen (stop-motion animator for movies like The 7th Voyage of Sinbad (1958)) and Ishirô Honda (director of Godzilla (1954) and many other kaiju features). Ironically, both men share May 7th as a significant day. Ishiro Honda was born on May 7th, 1911. Ray Harryhausen died on May 7th, 2013.
The set was built as a non destroyed Hong Kong, then destroyed and redressed to play as a different area, post-monster battle. The Hong Kong set was used as four different streets and sets, with the placement and dressing of elements changed each time.
Even though the film makers stated repeatedly that they did not want to reference any other mecha or kaiju works, they have admitted to accidentally doing so. For example, "jaeger" is also the name of one of the mech designs from the FASA mechcommander universe of the Inner Sphere faction. Also, the scene with Otachi searching for Dr. Newton Geizler is very reminiscent of the film The War of the Gargantuas (1966), during which a giant monster looks for a main human character who is hiding underground.
Two actors who were considered for this movie, got to be in similar movies ("military personnel versus alien invasion" theme) around the same time: Taylor Kitsch (considered for Raleigh) in Battleship (2012) and Tom Cruise in Edge of Tomorrow (2014).