The film's voice cast includes Ryunosuke Kamiki, Nanami Sakuraba, Mitsuki Tanimura, Sumiko Fuji, and Ayumu Saitō.

The film tells the story of Kenji Koiso, a timid eleventh-grade math genius who is taken to Ueda by twelfth-grade student, Natsuki Shinohara to celebrate her great-grandmother's 90th birthday.

The real-life city of Ueda was chosen as the setting for Summer Wars as part of the territory was once governed by the Sanada clan and was close to Hosoda's birthplace in Toyama.

[5] Kenji Koiso 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.

He also meets Wabisuke Jinnouchi, 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.

Wabisuke reveals that he invented the program and sold it to the United States Armed Forces for a test run and expanding it into a virtual intelligence.

Kenji, Sakuma, and most of the Jinnouchis form 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.

Natsuki wagers the 150 million avatars given to her in a single hand and critically injures Love Machine, prompting it to redirect the Arawashi towards Sakae's estate.

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.

[12] While visiting Ueda, Hosoda thought that Takeshige, who has previously worked with Studio Ghibli, should draw traditional Japanese houses for the film.

[16] 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.

[22] 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.

[33] 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.

[34] 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.

[37][38] To celebrate the 10th anniversary of the release of Summer Wars, Studio Chizu announced in November 2019 that a 4DX version of the film would be shown in select theaters in Japan beginning on January 17, 2020.

[43] 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".

[44] 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 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.

"[45] 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."

"[45] The Korean newspaper Herald Business saw the film's fantasy theme and gorgeous animation as a differentiator from works produced by Hollywood studios.

[31] 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."

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.

[49] 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."

[50] 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."

"[53] 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."

"[55] 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.

[63][64] 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,[63] 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.

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.

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.

[78][79] 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.