Farplane

The Farplane (異界, Ikai?, lit "other world") is the final resting place for the people of Spira. Summoners send the souls of the dead to the Farplane using a ritual dance called the sending". A gateway to the Farplane, through which the living may travel back and forth, is located in Guadosalam, where the Guado look after the Farplane. Those who journey here can summon an image of a dead person by thinking about them. It is believed by the Al Bhed that this phenomenon is a result of pyreflies reacting to peoples' memories, but no image of a living nor unsent person has ever been seen on the Farplane. This lends to an alternate belief that while images form due to pyreflies reacting to the memories of the living, only the images of those whose pyreflies (spiritual energy) are actually present in the Farplane can be seen there. Indeed, in Final Fantasy X, neither the images of Lady Ginnem nor of Seymour Guado can be seen on the Farplane until after the two unsent individuals have made their way to the Farplane.

In Final Fantasy X-2, it is revealed that the Farplane is actually the heart of Spira, and that it contains a potentially limitless amount of spiritual energy. The unsent Shuyin used an enormous machina called "Vegnagun" to drill extra-planar tunnels from the Farplane to Spira. These tunnels ended at each of the Chambers of the Fayth, and out of the tunnels poured hundreds of fiends, influenced by the malice and despair of Shuyin. These fiends were put down with the help of the Gullwings, and Shuyin was later defeated.