Kanon (カノン) is a Japanese adult visual novel developed by Key released on June 4, 1999 for Windows PCs. Key later released versions of Kanon without the erotic content, and the game was ported to the Dreamcast, PlayStation 2 and PlayStation Portable. The story follows the life of Yuichi Aizawa, a high school student who returns to a city he last visited seven years prior, and he has little recollection of the events from back then. He meets several girls and slowly regains his lost memories. The gameplay in Kanon 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 once ranked as the second best-selling PC game sold in Japan, and charted in the national top 50 several more times afterwards. Kanon has sold over 300,000 units across several platforms.
Following the game's release, Kanon made several transitions into other media. Two manga series were serialized in Dengeki Daioh and Dragon Age Pure. Comic anthologies, light novels and art books were also published, as were audio dramas and several music albums. Toei Animation produced a 13-episode anime television series in 2002 and an original video animation (OVA) episode in 2003. Kyoto Animation produced a 24-episode anime series in 2006. The 2006 anime was licensed and dubbed in English by ADV Films in 2008, but the license was given to Funimation after ADV's closure. The 2006 anime plays on the association between Kanon and the musical term canon by using Pachelbel's Kanon D-dur, or Canon in D major, as a background piece at certain instances throughout the series.