As some fans of Final Fantasy VII, X and X-2 may or may not know, the worlds of the two games share a plot-related connection. The connection's existance was established during an interview with Yoshinori Kitase (lead developer of the Final Fantasy series) and Kazushige Nojima (the scenario writer of Final Fantasy VII, Before Crisis, Advent Children, Final Fantasy VIII, Final Fantasy X, Final Fantasy X-2 and the Kingdom Hearts series) in 2002, as featured in the Final Fantasy X Ultimania Omega guidebook, an official Square-Enix publication.
This interview established that there would be a connection between the two
worlds, though it didn't detail it. However, based on what was later revealed
to be the connection, it's clear that it had already been conceived, as
Kitase hints at it with his final word on the subject. In 2003, the exact
nature of the concept was finally revealed in the Final Fantasy X-2 Ultimania,
having been hinted toward by a few elements of the game.
Nojima revealed that Shinra of the Gullwings, an Al Bhed child prodigy and
inventor of various machinery, would attempt using the remains of Vegnagun --
the behemoth machina Shuyin tried to destroy Spira with -- to extract life
energy from the Farplane and use it to power machines. Shinra would attempt
doing this as a result of his analysis of the Farplane late in the game.
During this diagnostic, Shinra concluded that there was a great deal of energy
floating around inside the Farplane, and that it was most likely the life
force of Spira, which could be extracted and used as a power source; however, he concluded that it would take generations to properly implement the idea.
Further of note is that Nojima explained that the Al Bhed entrepeneur Rin also
was interested in extracting mako from the Farplane, and that he provided
Shinra with the funding to make the attempt. For his part, Rin's desire to do
this is revealed during the game should he be uncovered as the culprit behind
covering up the malfunctioning machina disaster on the Mi'hen Highroad.
Nojima went on to say that Shinra's attempts to use Vegnagun's remains failed and that he was unable to complete the concept of mako-extraction, just as Shinra had predicted. However, some 1000 years later, once space travel became possible, Shinra's descendants would go on a voyage to the world of Final Fantasy VII. There, at some point in the future, they would be successful in utilizing the concept, and would provide electricity from the Planet for a price; these descendants would found the Shin-Ra Company of Final Fantasy VII.
The connection would again be hinted toward in the Final Fantasy X-2:
International+Last Mission (released in 2004) game's Last Mission scenario, in
which Rikku revealed that Rin and Shinra had begun working together. Next,
the Final Fantasy VII Ultimania Omega guidebook (released in September, 2005) also brings forth mention of the concept, and, finally, the connection may have received further indication through Dirge of Cerberus (released in
January, 2006) and the Advent Children Reunion Files book (released in May,
2006), in which it is established that the Shera airship seen in Advent
Children and Dirge of Cerberus runs on ancient, lost non-mako technology that
Cid discovered. This technology very well may have originally belonged to
Shinra's descendants, as they are the only previous inhabitants of VII's world
indicated to have been in possession of advanced technology, and because the interior of the Shera bears some aesthetic resemblances to those of the
Fahrenheit and Celsius airships that figure prominently into FFX and FFX-2
(though the Shera's interior bears more of a resemblance to the Celsius').
