The gameplay of Clannad follows a branching plot line which offers pre-determined scenarios with courses of interaction, and focuses on the appeal of the five female main characters by the player character. The game was ranked as the best-selling PC game sold in Japan for the time of its release, and charted in the national top 50 several more times afterwards. Key went on to produce an adult spin-off titled Tomoyo After: It's a Wonderful Life in November 2005, which expanded on the scenario of Tomoyo Sakagami, one of the five heroines from Clannad. Clannad has made several transitions to other media. There have been four manga adaptations published by ASCII Media Works, Flex Comix, Fujimi Shobo and Jive. Comic anthologies, light novels and art books have also been published, as have audio dramas and several albums of music. An animated film by Toei Animation was released in September 2007, followed by two TV anime series including two original video animation (OVA) episodes by Kyoto Animation produced between 2007 and 2009. Both anime series and their accompanying OVAs are licensed by Sentai Filmworks and were released in North America in 2009. The animated adaptations have received high sales figures in Japan as well as critical acclaim abroad.
On March 15, 2007, the Japanese television station BS-i announced a Clannad anime series via a short 30-second teaser trailer that was featured at the end of the final episode of the second Kanon anime series. Clannad is produced by Kyoto Animation and directed by Tatsuya Ishihara, who also worked on other adaptations of Key's visual novels Air, and Kanon. The anime aired between October 4, 2007 and March 27, 2008, containing 23 aired episodes out of a planned 24; the broadcast time was first announced on August 11, 2007 at the TBS festival Anime Festa, which is also when the first episode was showcased. The anime series was released in a set of eight DVD compilations released between December 19, 2007 and July 16, 2008 by Pony Canyon, with each compilation containing three episodes. Of the 24 episodes, 23 were aired on television with the first 22 being regular episodes, followed by an additional extra episode. The last episode was released as an original video animation (OVA) on the eighth DVD on July 16, 2008 and is set in an alternate universe from the anime series where Tomoya and Tomoyo are dating, which is based on Tomoyo's scenario in the game. The OVA episode was previewed on May 31, 2008 for an audience of four-hundred people picked via a mail-in postcard campaign. A Blu-ray Disc (BD) box set of Clannad was released on April 30, 2010. After the ending of the 23rd episode of the first Clannad anime series, a 15-second teaser trailer aired promoting a second season titled Clannad After Story. The anime is again animated by Kyoto Animation, and animates the After Story arc from the visual novel, which is a continuation of Nagisa's story, into 24 episodes. The same staff and cast from the first anime were used and the series broadcast in Japan between October 3, 2008 and March 26, 2009. Of the 24 episodes, 22 are regular episodes, the 23rd is an extra episode, and the last episode is a summary episode showcasing highlights from the series. The episodes were released on eight DVD compilation volumes between December 3, 2008 and July 1, 2009. The eighth DVD volume came with an additional OVA episode set in an alternate universe from the anime series where Tomoya and Kyou are dating. The OVA episode was previewed on May 24, 2009 to a limited number of people. A BD box set of Clannad After Story was released on April 20, 2011 in Japan with English subtitles.
The license holding company Sentai Filmworks licensed the Clannad anime series, and ADV Films localized and distributed the television series and the OVA starting with the first half season box set consisting of 12 episodes with English subtitles, Japanese audio, and no English language track, which was released on March 3, 2009. The second half season box set containing the remaining episodes was released on May 5, 2009. Sentai Filmworks licensed the Clannad After Story anime series; Section23 Films localized and distributed both the television series and OVA starting with the first half season box set with English subtitles released on October 20, 2009. The second half box set was released on December 8, 2009. Sentai Filmworks re-released Clannad in a complete collection set on June 15, 2010, which featured an English dub, produced at Seraphim Digital. The English dub premiered on March 25, 2010 on the Anime Network. Sentai Filmworks re-released Clannad After Story with an English dub on April 19, 2011, and re-released Clannad on BD in November 2011. The opening theme for the first season is "'Mag Mell' (cuckool mix 2007)" by Eufonius, a remix of the song "'Mag Mell' (cockool mix)", featured on the third disc of the game's original soundtrack, which is itself a remix of the game's opening theme "Mag Mell" (メグメル Megu Meru?). The first season's ending theme is "Dango Daikazoku" (だんご大家族 The Big Dango Family?) by Chata. It carries the same tune as "Chiisana Tenohira" (小さなてのひら Small Palms?), the ending theme from the After Story arc of the game. The second season's opening theme is "Toki o Kizamu Uta" (時を刻む唄 A Song to Pass the Time?) which uses the same tune as the background music track "Onaji Takami e" (同じ高みへ To the Same Heights?) from the game's soundtrack. The ending theme is "Torch", and both the opening and ending themes are sung by Lia. The rest of the soundtrack for both anime series is sampled from several albums released for the Clannad visual novel including the Clannad Original Soundtrack, Mabinogi, -Memento-, Sorarado, and Sorarado Append. The cover art for Sorarado Append is also visible as the last shot in the ending video animation of the first season.
Clannad's story revolves around Tomoya Okazaki, a third year high school student who dislikes his life. Tomoya's mother (Atsuko) died when Tomoya was young, leaving his father (Naoyuki) to raise him. After the accident, Tomoya's father turned to alcohol and gambling, and had frequent fights with his son. One day, Naoyuki, while arguing with his son, slammed Tomoya against the window, dislocating Tomoya's shoulder. Ever since then, his father has treated Tomoya nicely, but distantly, as if Tomoya and he were strangers rather than a family. This hurts Tomoya more than his previous relationship with his father, and the awkwardness of returning home leads Tomoya constantly to stay out all night. Additionally, the injury disables Tomoya from participating in his basketball club, and pushes him to distance himself from his school and other activities. Thus his delinquent life begins. Tomoya's good friend Youhei Sunohara, who got thrown out of the soccer club for a dispute, is also a delinquent and often hangs out in his dorm room with Tomoya doing nothing much. The story opens on Monday April 14, 2003 at the beginning of the school year, when Tomoya meets by chance Nagisa Furukawa, a soft-spoken girl one year older than he is who is repeating her last year in high school due to being sick much of the previous year. Her goal is to join the drama club which she was unable to do due to her sickness, but they find that the drama club was disbanded after the few remaining members graduated. Since Tomoya has a lot of time to kill, he starts to help Nagisa in reforming the drama club. During this period, Tomoya meets and hangs out with several other girls who he gets to know well and help with their individual problems.
In the second part of the story, which starts immediately after the end of the first part but extends into the next seven years, Tomoya and Nagisa start living together and get married. Tomoya has to endure several hardships that the family has been suffering from, mainly involving Nagisa's illness. Just after Nagisa gives birth to their daughter Ushio, Nagisa dies of her illness, leaving Tomoya to fall into a state of depression. This causes Nagisa's parents, Akio and Sanae, to look after Ushio. Five years later, Tomoya meets Shino Okazaki, his paternal grandmother. Shino explains to Tomoya about his father's past and tragedy, similar to Tomoya's current situation after Nagisa's death. After hearing that, Tomoya decides to raise Ushio and acknowledge Naoyuki as his father. Shortly after Tomoya regains his purpose for living, Ushio is struck with the same disease as Nagisa. Tomoya, Sanae and Akio struggle to save Ushio, with Tomoya retiring from his job, but all efforts are futile. In the coming winter, wanting to do anything for Ushio, Tomoya decides to take Ushio on a trip, but Ushio dies shortly after. Tomoya's psychology is developed in his dreams of a bleak world where small orbs of light float around called the Illusionary World (幻想世界 Gensō Sekai?). In the first few dreams, he sees a world devoid of all life except for one girl. Each time he dreams, he finds out more about the world. Tomoya discovers the girl has a special ability to fuse junk together to create new things, with which she creates a body for him. Thus he is reborn in this world, and fills time following the girl around. Tomoya conceives that only the two of them are "alive". To pass time, Tomoya and the girl try to build another doll with more junk they find, but as it has no soul, it fails to come to life. Remembering a distant world where he came from, Tomoya convinces the girl to build a ship so that the two can escape the approaching winter and continue a happy life. Eventually, winter sets in, and the girl becomes cold to the point where she cannot move any more. Upon meeting this tragedy, the girl tells Tomoya that he has another chance to go back and make things right. To do so, he must collect certain "lights" (symbols of happiness) similar to those floating around in the Illusionary World. If all the "lights" are collected throughout both story parts, a chance to save Nagisa from dying will become available, and the true ending where Nagisa survives and lives with Tomoya and their daughter Ushio will also become available.