In 1863, where an alternate nineteenth century Europe has made tremendous strides in steam-powered technologies, scientist Lloyd Steam and his son Edward have succeeded, after a lengthy expedition, in discovering a pure mineral water. They believe the water can be harnessed as an ultimate power source for steam engines (the main industrial engine of the time). An experiment in Russian Alaska goes terribly wrong, with Edward being engulfed in freezing gases, but results in the creation of a strange spherical apparatus.
Three years later, back in England, Edward's son, Ray Steam, is an avid young inventor who works at a textile mill in Manchester as a maintenance boy, often working on a personal steam-powered monowheel at home. While he usually lives alone with his mother, his friend Emma and her brother Thomas have recently been sent over to stay until their mother returns from a business trip.
Ray's life is suddenly disrupted by the arrival of a package from his grandfather Lloyd; the metallic ball seen earlier, along with its schematics and a letter instructing him to guard it. Then, Alfred and Jason, two members of a company called "The O'Hara Foundation" arrive and attempt to steal the sphere, but Lloyd appears just in time to distract them, allowing Ray to escape with the package.
With Emma's help, he manages to activate his monowheel as more agents, operating a large steam automotive, give chase, succeeding in thwarting it on a railway line by putting it in the way of an incoming train. By coincidence, Robert Stephenson, who was the intended recipient of the Steam Ball, was on his way to Manchester to meet with the elder Dr. Steam, and happens to be on the train. However, as the train approaches the station, a zeppelin carrying Alfred descends over their compartment and kidnaps Ray, taking the ball with them.
Arriving in London sometime prior to the 1866 Great Exhibition, during a dining session Ray meets Scarlett O'Hara, the spoiled granddaughter of the Foundation's head chairman; Archibald Simon, an administrator of the company; and finally his father Edward, who has been partially mechanized for his severe injuries from the Alaskan experiment. He promptly takes Ray (and an insistent Scarlett) on a tour of the "Steam Castle"; an elaborate facility run by an army of engineers, and entirely powered by the compressed gas in three "Steam Balls", one of which was the one sent to Ray. He is enamored both by the castle, and his father's vision of using it to enlighten mankind. Ray is then quickly recruited to help complete the castle, and begins developing a love/hate friendship with Scarlett, who has become attracted to him.
Ray later encounters Lloyd again, who has escaped from his cell in the castle and is attempting to sabotage it from within, knowing that Eddie's intentions for it were evil. The Foundation's true intentions for the exhibition is to sell weapons to Britain's enemies. Upon discovering an arsenal of war machines in its underbelly, Ray struggles with the moral dichotomy of being a scientist - of how to contribute to the world without giving into vanity, conveying his conflict towards his father, and the one brewing between Eddie and Lloyd.
The two eventually reach the core section of the castle, and manage to pry away one of the Steam Balls before security surrounds them. Lloyd is shot by Alfred and recaptured, while Ray makes another elaborate escape with the ball. The next morning, the exhibition is underway, and Ray has reunited with Robert Stephenson, giving him the ball and the knowledge he acquired in captivity. An assault on the castle is then met with a demonstration by the Foundation of its new steam-powered weapons, which turn the exhibition into a war zone. Ray becomes aware of his folly when Stephenson uses the ball to enhance his own company's battle tanks (which resemble the real-life Hornsby Chain Tractor of 1905), leading him to realize that he had no better intentions than the Foundation's.
Eddie, eager to show the world the castle, enters the observation/control room and orders the engineers to "launch" it, causing the structure to rise and shed its decorative outer shell, revealing a monstrous floating fortress, the steam generated by the structure's gigantic propulsion jets flooding the city and freezing everything in its path.
Ray steals the ball again to create a makeshift rocket vehicle, and attempts to gain entry as the British Royal Navy attempts in vain to shoot it down. Stephenson attempts to hold back the castle by shooting chains at it and pulling it back with steam locomotives. This attempt works for a few moments, but eventually all the chains snap from the strain.
Scarlett has since become worried about Ray, and has found herself trapped in the castle whilst searching for him. She is in the control room with Eddie as Ray arrives, and Lloyd (having escaped again) confronts Eddie about his actions before shooting him with a stolen gun, and having his body disappear in a cloud of steam.
With the castle steered off course from the battle, the structure has become unstable and threatens to explode over the city. Lloyd and Ray rush to redirect the castle over the Thames, defeating Alfred, who is controlling a pair of gigantic construction claws in the process. At the last minute Eddie, whose metal body repelled the gunshot, appears alive and decides to lend a hand. Ray re-installs the stolen steam ball, and makes his way to the control room to make a final escape with Scarlett on an emergency jet pack, while Eddie and Lloyd halt the machine over the Thames and leave as well. The castle eventually detonates in a spectacular explosion, sparing the city of most of the destruction.
The ending montage reveals Ray returning home, and later becoming a global superhero (aka Steamboy) using the jet pack gear from the castle; his grandfather Lloyd introducing Ray to electricity and finally passing away; the Great War being fought with paratroopers and zeppelins; his father Eddie founding a corporate conglomerate; and Scarlett maturing and becoming a famous pilot.James Ray Steam (ジェームス・レイ・スチム, Jēmusu Rei Suchimu)
Voiced by: Anne Suzuki (Japanese); Anna Paquin (English)
The main character, a 13-year-old boy living in Manchester, is an inventor following the paths of his father and grandfather. He possesses a mechanical talent that was inherited from his family, and demonstrates this in at least two instances by building a steam-powered monowheel and a steam-propelled flying device. He has a youthful idealism and sincerely dislikes the employment of technology for harmful purposes. During the film his motivations are alternately swayed by the influences of his father and grandfather.
Scarlett O'Hara St. Jones (スカーレット・オハラ・セントジョーンズ, Sukāretto Ohara Sentojōnzu)
Voiced by: Manami Konishi (Japanese); Kari Wahlgren (English)
Selfish, spoiled, misguided, yet whimsical and not completely heartless; she is the American 14-year-old granddaughter of the chairman of the O'Hara Foundation. She matures as a result of her encounter with Ray. Her character is based upon the fictional character of the same name, from the novel Gone with the Wind
Lloyd Steam (ロイド・スチム, Roido Suchimu)
Voiced by: Katsuo Nakamura (Japanese); Patrick Stewart (English)
Ray's idealistic grandfather. The original conceiver of the Steamball, which he succeeds in developing with his son Edward. Lloyd's pursuit of progress without much regards to safety and ignorance of Eddy's pleading directly leads to his son's disfigurement. A difference of opinions with his son Edward leads to friction between them. While Edward believes that science is an instrument of power, Lloyd simply wishes to use it to help people. They both develop distinctly different visions for their ultimate invention, the Steam Castle. It is later revealed that Lloyd intended the Steam Castle to be a sort of flying amusement park, but Eddy scoffed at such a premise, denouncing it as a "fairy tale vision". Edward instead built the Steam Castle as a flying military fortress.
Edward Steam (Eddy) (エドワード・スチム（エディ）, Edowādo Suchimu (Edi))
Voiced by: Masane Tsukayama (Japanese); Alfred Molina (English)
Ray's father. The accident that occurred in the development of the Steamball left Edward in a state where he needed to have machinery replace some of his body, including his right arm and parts of his legs. It left him not only physically disfigured, but it severely twisted his morals as well, driving him to believe that science is an expression of mankind's ultimate power. Edward's father calls him Eddy. He uses the Foundation and the Exhibition as a springboard to launch his ultimate invention: a monstrous, flying war machine called the Steam Castle.
Robert Stephenson (ロバート・スチーブンスン, Robāto Suchībunsun)
Voiced by: Kiyoshi Kodama (Japanese); Oliver Cotton (English)
Edward and Lloyd Steam's friend and rival, a major player in the Industrial Revolution. He claims that he wishes to use the Steam Ball for the good of the British Empire, but exactly how
he plans to do it is questionable. Possibly based upon the real-life Robert Stephenson.
David (デイビッド, Deibiddo)
Voiced by: Ikki Sawamura (Japanese); Robin Atkin Downes (English)
Young, talented engineer and Robert Stephenson's loyal right hand. His kindness does not betray a thirsty ambition.
Archibald Simon (アーチボルド・サイモン, Āchiborudo Saimon)
Voiced by: Satoru Sato (Japanese); Rick Zieff (English)
The O'Hara Foundation's chairman's representative, whose duties also seems to be Miss Scarlett's caretaker and personal servant; he is overweight and wears glasses. Grossly obsessed with money, he continues to market his wares even when his life is in danger, with comical results.
Alfred Smith (アルフレッド・スミス, Arufureddo Sumisu)
Voiced by: Susumu Terajima (Japanese); Mark Bramhall (English)
The smarter of the two O'Hara thugs, Alfred works with Jason in trying to steal the Steamball. He outlives his oafish companion, and seems to hate Ray even more. He, along with Jason, performs much of Simon's dirty work. The two of them capture Ray and bring him to London, and later attempt to kill him. Alfred does so by trying to smash him with a construction crane, but Ray deftly avoids it, causing it to slam into Alfred instead.
Jason (ジェイソン, Jeison)
Voiced by: Tetsu Inada (Japanese); David S. Lee (English)
One of the men working in the O'Hara Foundation in the United States of America. Jason and Alfred were the ones that want to get the Steamball. However, Ray Steam is kidnapped. He represents the more brutish half of the two O'Hara thugs, and engages in a vicious aerial battle with Ray toward the end of the movie.
Ray's Mother (レイの母親, Rei no Hahaoya)
Voiced by: Keiko Aizawa (Japanese); Kim Thomson (English)
Ray's mother who volunteers as a teacher for the neighbouring children (as seen at the beginning of the movie).
Emma (エマ, Ema)
Voiced by: Sanae Kobayashi (Japanese); Paula J. Newman (English)
A friend of Ray's.
Thomas (トーマス, Tōmasu)
Voiced by: Aiko Hibi (Japanese); Moira Quirk (English)
The AdmiralVoiced by: Osamu Saka (Japanese); Oliver Muirhead (English)
Highly decorated and a Knight of the Order of the Garter, the Admiral is Robert Stephenson's main point of contact with the British Government. The Admiral is rather set in his ways, believing that men, not machines, fight wars. He displays a stereotypically British style of composure, calmly taking afternoon tea on the deck of his flagship while a battle rages nearby.
The Japanese release of Steamboy featured the voices of Anne Suzuki, Manami Konishi and Masane Tsukayama. The United States release, held in a limited number of U.S. theaters on March 18, 2005, and expanded to additional theaters on March 25, was released in two formats: a subtitled release featured in fewer cinemas, and an English dubbed version cut down by 15 minutes that featured the voices of Anna Paquin, Alfred Molina, and Patrick Stewart.
Steamboy was distributed across Japan by Toho and English regions by Sony's Triumph Films subsidiary. The DVD was released in Japan on April 15, 2005, in Australia on June 22, 2005, the USA on July 26, 2005, and the UK on March 27, 2006. Both the edited English version and the original Japanese version were made available on DVD, with the longer version being sold as the Director's Cut.
Steamboy was later adapted into a video game for the PlayStation 2 in Japan by Bandai. (Development by Cavia and SIMS)
Steamboy was the 2004 recipient of Best Animated Feature Film at the Sitges - Catalan International Film Festival. The film received mixed reviews from critics.
Stephen Hunter of The Washington Post states, "The movie never transcended its elaborate production work to achieve an independent reality. It's simply pictures of what could have happened."
Review aggregation website Rotten Tomatoes gave Steamboy a rating of 60% based on 89 reviews, with the site's consensus "The story isn't the greatest, but there's an abundance of sci-fi eye candy to compensate."
The film was not a box office success in the United States.
According to the reviewer KJB at IGN.com, this could be due to the marketing methods used in the United States. Steamboy could have had a larger Western audience, but due to the limited release, that was not able to happen. "Steamboy is one of those few anime films that would be able to play to a wide audience in the United States. Instead, the film is getting a limited release through Sony's smaller label, skipping some cities entirely and only playing in smaller art houses in many of the cities that are getting the film."