Fandisc

A fan disc (sometimes called fandisk or simply abbreviated as FD) is a package of additional content, usually released by a game company after the successful launch of one of its titles. The contents of fan discs varies, but often includes new images, music, minigames and miscellaneous information related to the original game. Sometimes, fan discs will also feature whole new games in order to extend the original title's storyline; however, those are rarely considered true sequels, often depicting events of minor importance to the overreaching plot of the series and being considerably short. Alternatively, it is not uncommon for such games to present "What If" scenarios, retell certain events from the point of view of a different character or transport the main cast to a different setting.

Eroge visual novels, such as Popotan, frequently receive fan discs. Since most visual novels depict standalone stories, rarely warranting sequels, this particular genre notoriously employs fan discs as a medium to explore pre-established settings and profit from the original game's popularity. Sometimes, a fan disc is made as a compilation of the two separate, but similar games, aiming to serve as a link between them (the Come See Me Tonight series being an example).

Due to their nature, however, fan discs rarely receive fan-translations, even among those based on critically acclaimed titles: Since their contents are not required to the enjoyment of the original piece, most active translation groups prefer to move on to another projects involving full length games, especially if proper sequels have been released.

Tsukihime's PLUS-disc translation by mirror moon, MangaGamer's first official English translation of the Edelweiss fan disc, Edelweiss Eiden Fantasia, and Jutsuki Sen & Co.'s partial patch of Muv-Luv: Altered Fable are notable examples of high-quality projects dedicated to make fan discs accessible to audiences unfamiliar with the Japanese language.

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Wikipedia