Kenji Koiso (Ryunosuke Kamiki) is a young student at Kuonji High School with a gift for mathematics and a part-time moderator in the massive computer-simulated virtual reality world OZ along with his friend Takashi Sakuma (Takahiro Yokokawa).
One day, Kenji is invited by fellow Kuonji student Natsuki Shinohara (Nanami Sakuraba) to participate in the 90th birthday of her great-grandmother Sakae Jinnouchi (Sumiko Fuji). After traveling to Sakae's estate in Ueda, Natsuki introduces Kenji as her fiancé to Sakae, surprising them both. Kenji meets several of Natsuki's relatives and discovers that the Jinnouchis are descendants of a samurai (vassal of the Takeda clan) who challenged the Tokugawa clan in 1615. He also meets Wabisuke Jinnouchi (Ayumu Saitō), Natsuki's half-great-uncle and a computer expert who has been living in the United States since stealing the family fortune 10 years ago.
Kenji receives an e-mail with a mathematical code and cracks it. Love Machine, an artificial intelligence written by Wabisuke, uses Kenji's account and avatar to hack the infrastructure, causing widespread damage. Kenji, Sakuma, and Natsuki's cousin Kazuma Ikezawa (Mitsuki Tanimura) confront Love Machine. Love Machine defeats Kazuma's avatar King Kazma and continues to consume accounts in the OZ mainframe, creating catastrophic traffic congestion and disabling electrical devices. Two of Sakae's relatives, Rika (Sakiko Tamagawa) and Shota Jinnouchi (Yutaka Shimizu), discover Kenji's involvement. Shota arrests Kenji, but the congestion causes Natsuki to return them to the estate.
Sakae calls associates in important positions in Japanese society and relatives who work in emergency services, encouraging them to work their hardest to reduce chaos and damage, comparing the situation to war. Kenji is able to return control of the mainframe to the moderators and engineers. Wabisuke explains that he sold the program to the United States Armed Forces for a test run. After an argument with Sakae, Wabisuke leaves the estate. Sakae later encourages Kenji to take care of Natsuki during a Koi-Koi match.
The next morning, Sakae is discovered dead by Kenji and the Jinnouchis. Her youngest son Mansaku (Tadashi Nakamura) explains that she had angina, and that Love Machine had deactivated her heart monitor. Kenji, Sakuma, and most of the Jinnouchis initiate a plan to defeat Love Machine with a supercomputer using ice blocks as a coolant, while Natsuki and the others prepare a funeral for Sakae.
Kenji, along with Sakuma and the others, capture Love Machine, but Shota carries the ice blocks to Sakae's body, causing the supercomputer to overheat. Love Machine consumes King Kazma and redirects the Arawashi Asteroid Probe onto a collision course with a nuclear power plant. Meanwhile, Natsuki discovers a will left by Sakae and reunites with Kenji and the rest of the group. Natsuki has Wabisuke return home before the family reads Sakae's will, asking them to bring Wabisuke back to their lives. Realizing that Love Machine sees everything as a game, Kenji has the Jinnouchis confront Love Machine to play Koi-Koi in OZ's casino world, wagering their accounts in a desperate attempt to stop Love Machine. Natsuki wins several rounds, but gets distracted and nearly loses her "winnings".
However, OZ users worldwide enter their own accounts into the wager on Natsuki's side, which also prompts the guardian programs of OZ—the blue and red whales known as John and Yoko—to upgrade Natsuki's account. Natsuki wagers the 150 million avatars given to her in a single hand and critically damages Love Machine, prompting the artificial intelligence to redirect the Arawashi towards Sakae's estate. Kenji attempts to break into the probe's GPS, while Wabisuke disables Love Machine's defenses. After being revived and assisted by several of the Jinnouchi family's avatars, King Kazma destroys Love Machine. Kenji activates the GPS code to redirect the Arawashi away from the estate, destroying the estate's entrance and causing a geyser to erupt. In the aftermath, the Jinnouchi family, celebrating their victory as well as Sakae's birthday, has Natsuki kiss Kenji after they confess their love to each other.
After the critical and commercial success of The Girl Who Leapt Through Time, Madhouse was offered to produce another film. Whereas Madhouse based the previous film on a novel, the studio was given the chance to create the next film. Director Mamoru Hosoda selected a story for both people with family and those without having a family. Production of Summer Wars commenced in 2006.
Most of the film is set in the real-life city of Ueda. Ueda was chosen as the primary setting of the film because it is located in a territory formerly governed by the prominent Sanada clan, upon which the Jinnouchi family is based. Ueda is also close to Hosoda's birthplace in Toyama. Hosoda's inspiration for the name of the social network OZ came from a large supermarket that he once visited while still working for Toei Animation at the time. Although noting similarities between OZ and Second Life, Hosoda also cited the Japanese social networking website mixi as a primary influence because of his experiences. For the color and design of OZ, he cited Nintendo games as inspiration. The design aesthetic was compared by some reviewers to the appearance of OZ. Hosoda said that he admires the artwork of Takashi Murakami, but designed the social network as a "clean, uncluttered look." During production, Hosoda visited his then-fiancé's house in Ueda, and experienced the history of her family's life. Hosoda cited his influence of using a family as the basis of the film from his marriage and from attending several film festivals.
In addition to Hosoda, the team included writer Satoko Okudera and character designer Yoshiyuki Sadamoto, who previously worked with Hosoda on The Girl Who Leapt Through Time. Hiroyuki Aoyama served as an animation director, while action animation direction was handled by Tatsuzo Nishida. During production, Sadamoto based Wabisuke's design on those of actor Yusaku Matsuda. Aoyama was responsible for supervising the animation of the real world scenes, while Nishida supervised the animation for the digital world, using both traditional animation and computer animation techniques. Digital animation studio Digital Frontier was responsible for creating the visuals of OZ and its avatars. Youji Takeshige oversaw the art direction for Summer Wars. While visiting Ueda, Hosoda thought that Takeshige, who has previously worked with Studio Ghibli, should draw traditional Japanese houses for the film. The film also features the Japanese spacecraft Hayabusa, whose control center is located in the nearby city of Saku. Hosoda included the spacecraft to support Japan's contribution towards space exploration.
The film was announced at the 2008 Tokyo International Anime Fair. At the 2009 Otakon convention Madhouse president Masao Maruyama said that Hosoda insisted on including 80 family members as its main characters. Maruyama then quipped that he asked Hosoda to promise only two main characters and two years of production for his next film. Summer Wars was one film in Madhouse's larger theatrical film release strategy, to release one new film each season for the next year. The release of Summer Wars was followed by Mai Mai Miracle and Yona Yona Penguin in 2009 with Redline released during the first half of 2010.
Akihiko Matsumoto composed the score for Summer Wars, with Randy Miller providing the additional music. The soundtrack of the film, titled Summer Wars Original Soundtrack (「サマーウォーズ」 オリジナル・サウンドトラック, Samā Wōzu Orijinaru Saundotorakku), was released by VAP on July 9, 2009. The release consists of 18 tracks. It remained on the Oricon music charts for four weeks and peaked at No. 112.
The film's theme song, titled "Bokura no Natsu no Yume" (僕らの夏の夢, lit. "Our Summer Dream"), was written and performed by Tatsuro Yamashita. It was released by Warner Music Japan as a maxi single on August 19, 2009. The single included two other songs by Yamashita that are unrelated to the film. The first two songs have corresponding karaoke versions, and the third song is recorded from a live performance. The single peaked at 8th place on the Oricon charts.
A high level of anticipation surrounded Summer Wars before its release, due to the critical and popular success of The Girl Who Leapt Through Time. Kadokawa Shoten promoted the film online through their official YouTube channel, aiming at international as well as domestic fans. On April 8, 2009, a one-minute high-definition (HD) trailer was released followed by a longer trailer on June 16. On July 29, the Japanese website of Yahoo! Movies streamed the first five minutes of the film and Kadokawa offered the footage on their YouTube channel several days later to allow for international viewing. It also offered two of the film's 15-second television adverts online. Before its release Masao Maruyama believed that "the film should be pretty popular, since the pre-sales for the tickets are very high".
Iqura Sugimoto's manga adaptation of the film was featured in the July 2009 debut issue of Kadokawa's manga magazine Young Ace. The first compilation volume of Sugimoto's work was released in Japan on August 10 and debuted in 23rd place on the Oricon comic ranking, selling 51,645 copies. The second volume was released on February 4, 2010, and debuted in 12th place, selling 53,333 copies. Sugimoto's manga was licensed into English by Vertical in January 2013, and the two volumes were released on October 22, 2013 and December 17, 2013. An additional manga side story was featured in the July 2009 issue of Comp Ace magazine.
Summer Wars premiered in Japan on August 1, 2009. The film was distributed in South Korea by CJ Entertainment where it premiered on August 12. Cathay Organisation released Summer Wars in Singapore on February 25, 2010. Mighty Media released the film in Taiwan on June 4, 2010. The film was released by Eurozoom in France on June 9, 2010.
Summer Wars had its North American premiere on February 26, 2010, as the opening night event of the annual New York International Children's Film Festival with director Mamoru Hosoda in attendance. Hosoda answered audience questions following the film's screening through an interpreter. Hosoda and a producer subsequently appeared at the Massachusetts Institute of Technology (MIT) Comparative Media Studies Program on March 1, 2010, where they offered a public screening free of charge and answered questions. The film was also screened at the IndieLisboa Film Festival. The debut screening in Australia was on June 14, 2010, as part of the Sydney Film Festival. It also screened at Melbourne International Film Festival on August 8, 2010. The Leeds International Film Festival showed the film on November 20, 2009, and the English dubbed version of the film premiered at the New York International Children's Film Festival on November 20, 2010. At Otakon 2010 Funimation Entertainment announced that a limited release of the film would begin in theaters on December 3, 2010, at the Gene Siskel Film Center.
Summer Wars aired on Adult Swim's Toonami block on December 14, 2013, with a rating of TV-14-LV. The film was watched by 1.36 million viewers. Summer Wars aired again on Toonami on December 6, 2014 after Hellsing Ultimate Episode 9.
Review aggregator Rotten Tomatoes reports that 77% of critics have given the film a positive review based on 22 reviews with an average rating of 7/10. At Metacritic,which uses a normalized rating system, the film earned a "generally favorable" level rating of 63/100 based on 12 reviews by mainstream critics.
Mark Schilling of The Japan Times rated the film 5 out of 5 stars and observed that Summer Wars "may contain familiar elements, beginning with its bashful, moonstruck young hero, but it combines them in ways fresh, contemporary and dazzlingly imaginative". He also said that the film provides a social commentary on the differences between an "analog world" and a "realm of digital devices". Schilling titled his article "The future king of Japanese animation may be with us; Hosoda steps out of Miyazaki's shadow with dazzling new film". He praised Sadamoto, Aoyama and Nishida for producing "scenes of animated spectacle that, in their dazzling fluency of motion and untethered brilliance of invention, makes the usual SF/fantasy anime look childish and dull". Twitch Film published a review by Guillem Rosset who also referenced Miyazaki noting that following The Girl Who Leapt Through Time "cries went out immediately hailing him [Hosoda] as the heir apparent". He claimed that with Summer Wars, "Hosoda is the new king, the best story teller working within the animated medium in Japan and – quite possibly – the world." Rosset praised the film itself as "richly detailed and beautifully written...gorgeous to look at." and "blessed with an extensive cast of stunningly detailed and authentic characters." He concluded by saying "Hosoda has perfectly balanced the need to entertain via the visuals with the rich and satisfying character work that separates him from the massive pack of quality technicians to establish himself as truly a master story teller." He also noted that "The wonderful cast of characters is one of the film's greatest strengths" while also highlighting that, of the virtual world of OZ, "Here the creative minds of Madhouse can let their imagination run wild." With regards to the technical aspects, Rosset called the film "a top class audiovisual show." He concluded by writing "Mamoru Hosada deserves a place as one of the top contemporary Japanese animators. And it's good to know that once the time comes for Miyazaki to retire (not too soon I hope!) there's people capable of following his steps." The Korean newspaper Herald Business saw the film's fantasy theme and gorgeous animation as a differentiator from works produced by Hollywood studios.
Patrick W. Galbraith of Otaku2.com compared the design of OZ to Takashi Murakami's artwork, specifically "the flatness, or slick, polished surfaces" and then contrasted them with the sequences in Nagano noting, "it has a warm and lived in feel to it, aided by a scrupulous attention to detail." Of the story and characters Galbraith wrote that "scenes such as the large family coming together and talking over dinner are heartwarming and hilarious." and compared the movie to "a moving picture book, a family photo album turned back a few decades." He also noted the audience response, reporting sold-out screenings two nights in a row, and highlighting handwritten notes left at the theater by "hoardes of fans who on the spot decided to move to Nagano" In conclusion, Galbraith wrote "there is an innocence and purity to this work that really reminds [him] of Miyazaki Hayao and Studio Ghibli back in the day, and the stellar backgrounds invoke Shinkai Makoto." Justin Sevakis of Anime News Network gave the film an 'A' rating and wrote that "decades from now, Summer Wars will be seen as the official arrival of [director] Mamoru Hosoda into the realm of historically important anime directors." He called the film "a near-perfect blend of social satire and science fiction, at once timely and timeless, sardonic and optimistic." and noted that the film is "practically overflowing with sharp social insight in a way we have not seen from anime in years." Sevakis praised Yoshiyuki Sadamoto's character designs and highlighted the visuals as "sharp and consistently great". In summing the film up he called Summer Wars "Incredibly entertaining, and intriguingly intelligent. Accessible and fast-paced. Pretty much perfect." Similarities have been commented on between the film and a previous work of Hosoda, Digimon Adventure: Our War Game. Neo magazine has stated that Our War Game is "plainly a prototype" of Summer Wars. Rachel Saltz of The New York Times also gave a positive review of the film. Saltz praised Mamoru Hosoda's direction, and says it "matches the clean, classically composed images of his [Hosoda's] outer story." She further praised the visuals and themes, comparing it to those of director Yasujirō Ozu. In his review for Variety critic Peter Debruge stated that Hosoda's direction "appeals to the hard-to-please teen crowd by taking mind-bending ideas and planting them within a relatable contempo context." He also praised the CG animation in the OZ sequences. Peter Hartlaub of the San Francisco Chronicle praised Hosoda's style and said that it "adds enough dimensions to his characters and kinetic battles that the serene real world seems like a dream state." He also likened Hosoda's style to that of Hayao Miyazaki and Nintendo. Hartlaub complained that Kenji's character is "a bit too over-caffeinated in the first part" and concluded that the film is "the kind of fun and quirky film that you don't see very often in art houses this time of year." Ty Burr of The Boston Globe gave the film 3 out of 4 stars. He stated that "Summer Wars is most appealing in its hushed moments" and also praised Satoko Okudera's writing, stating that it "stakes a claim for the non-virtual world of history and of family ties that stretch back to Japan’s medieval era." He also praised the OZ animation sequences as "visually ravishing explorations of white-on-white cyberspace, but the hectic gaming action sequences feel curiously passé." Burr notes that in the film, "it's what's old that's made to seem refreshingly new." In his review for the New York Post V.A. Musetto gave the film 2 out of 4 stars and called the film "great despite its structural problems". Musetto also complained about the storyline, stating that the "sci-fi elements seem silly rather than suspenseful." Nicolas Rapold of The Village Voice also praised the film's visuals, and said that "it’s hard to appreciate things like the character detail amid the insufferably squealy voicing and arbitrary suspense."
Kevin Thomas of the Los Angeles Times praised the film's visuals, stating that "Summer Wars is awesome in its detailed depiction of Oz, which floats in space with an array of satellites, and earthly cityscapes visited by calamities." Thomas also said the film is "also a superb example of Japanese anime, balancing science fiction fantasy with a paean to the timeless value of family life." and called it "a sophisticated yet poignant family entertainment with an appeal beyond Japanese animation buffs." Stephanie Merry of The Washington Post gave the film 2 out of 4 stars. Merry criticized the film's plot, stating that it "ventures into territory both melodramatic and corny." Merry also said that the relationship between Natsuki and Kenji "unfolds as blandly as a Debra Messing rom-com." Frank Scheck of The Hollywood Reporter stated that the "increasingly convoluted narrative may be too difficult to follow for younger viewers," but said that the film's "thematic ambition and dazzling visual style ultimately make it one of the more rewarding anime efforts to reach these [American] shores."
In Japan, Summer Wars ranked 7th in the box office, grossing an equivalent US$1,338,772 on 127 screens during its opening weekend, and ending its run with a total gross of $17,425,019. In South Korea, the film debuted in 8th place and earned an equivalent of US$369,156 on 118 screens with a total gross of $783,850. In Singapore, the film opened in 17th place and earned an equivalent of US$14,660 on 3 screens, and later concluded its run with a total gross $29,785. As of June 2010, the film went on to gross $18,353,560 worldwide. During the film's limited release in the United States, it grossed $1,412 and opened 76th at the box office in its opening weekend, later concluding its run with a total gross of $80,678.
Summer Wars was released in Japan on DVD and Blu-ray on March 3, 2010. The DVD version contains a 16-page booklet, OZ stickers, previews, interviews with the film's cast (Ryūnosuke Kamiki, Nanami Sakuraba, Sumiko Fuji, Mitsuki Tanimura and Ayumu Saitō) and an interview with director Mamoru Hosoda, while first press limited edition of the Blu-ray also included the same features, but also added hanafuda cards, an art book, and a film bookmark, and a making-of documentary. These releases were undertaken by Vap. In its first week of release the film became the top selling anime Blu-ray in Japan, with an estimated 54,000 copies sold and surpassed the previous record holder Evangelion: 1.0 You Are (Not) Alone. As of 2010, the film is the second highest Japanese Blu-ray debut overall, following Michael Jackson's This Is It. Based on pre-orders Summer Wars was expected to be eclipsed in sales by Evangelion: 2.0 You Can (Not) Advance on its release in May. Summer Wars also topped the Oricon Animation DVD charts with 55,375 copies sold in its first week. The Japanese Blu-ray release of Summer Wars was nominated for a Digital Entertainment Group of Japan (DEG Japan) Award for Best Interactivity. In Europe the DVD and Blu-ray was released on November 26, 2010, by Kazé. British distributor Manga Entertainment announced in January 2010 they had licensed Summer Wars for the United Kingdom, and was released in March 2011. In North America, Funimation released Summer Wars on DVD and Blu-ray on February 15, 2011. The North American DVD and Blu-ray releases included previews, and the interviews with Hosoda, Kamiki, Sakuraba, Fuji, Tanimura and Saitō. The first press copies included art cards. To get out enough copies to meet demand some did not ship with the OZ O-card (cardboard slip-cover), as it required specialty printing that takes longer to produce than the rest of the product. Funimation offered to send out the O-Card to customers who did not receive one as soon as they are available if they fill out a request form on their official website.
Summer Wars was the first Japanese animated film to be included as a competitor at the Locarno International Film Festival awards in Switzerland, where it was nominated for the 2009 Golden Leopard award. The film made its international premiere at the festival's celebration of manga, paying tribute to its impact on the animation industry. Although the film did not win the award the Swiss newspaper Tribune de Genève said it was, "by far, the best film we could find" in the competition and noted that the film would have been the logical winner given the festival's theme. The film was featured in the Sitges Film Festival in the Oficial Fantàstic Panorama category, where it won the Gertie Award for Best Animated Feature Film. Summer Wars received an award for new media from Japan's Ministry of Economy, Trade and Industry on October 24, 2009, at the Digital Content Association of Japan's annual convention. Summer Wars was also nominated for Best Animated Feature Film at the Asia Pacific Screen Awards, although it did not win. The film was awarded the Animation Division Grand Prize at the 13th Japan Media Arts Festival which Hosoda's The Girl Who Leapt Through Time won in 2006. Summer Wars won an Award of Excellence in Animation along with four other films at the 33rd Japan Academy Prizes. The Award of Excellence is in effect a nomination for the Animation of the Year Prize, which it won in the final ceremony on March 5, 2010. The film was shown at the 60th Berlin International Film Festival in February as part of the Generation 14plus program. Summer Wars won the Audience Award for Best Animation Feature at the Anaheim International Film Festival. Funimation, along with GKIDS, submitted the film for Best Animated Feature for the 83rd Academy Awards. The film was the 14th submission for the category. Summer Wars won the Best Animation Film Award at the 70th Mainichi Film Awards. Hosoda received an Annie Award nomination as Best Director, becoming the third Japanese individual, besides Hayao Miyazaki and Ghibli composer Joe Hisaishi, to be nominated in an individual Annie category since 2004.