There were some characters in the Kingdom Hearts series from Final Fantasy that didn't make the "final" cut. Here is a list.
Irvine Kineas was originally going to be alongsinde Selphie, but was replaced by Wakka.
Bahamut would've appeared as a summon, but was cut.
Tifa Lockhart would've appeared in the first title alongside Cloud, but got cut.
Rikku (She would've had Yuffie's role, but the deutragonist was already named Riku, so Yuffie needed to replace her & even take her design.)
Cloud, Cid, Leon, Yuffie, Aerith & Tifa would've been in Birth by Sleep, except "there were already too many plot lines, & it would've gotten confusing anyway", according to T.N.
Laguna Loire would've been the host of the Mirage Arena, so as to add some story to it. But they've been hemming & hawing over whether he should be in Dissidia 012 Duodecim Final Fantasy or KH Birth by Sleep, so they put him in DD012FF.
Vincent Valentine would've appeared alongside Cloud, but their appearances were too similar for the game, so only Cloud appeared.
There were some characters in the Kingdom Hearts series from Final Fantasy that didn't make the "final" cut. Here is a list.