FAQ for
Final Fantasy VII: Advent Children (2005)

No, it is a sequel set two years after the game.

She is but mostly in dream sequences with Cloud but she is seen at the very end of the movie

It has something to do with a mistranslation in the game; Aerith is actually the correct translation of the name. I think it's because that a "th" in Japanese is similar to an "s" and the name in Japanese is "Earisu" so it's one of the few translation mistakes the English versions of the games have. She is called "Aerith" in all future Final Fantasy VII projects.

If you watch the summary feature on the DVD with the subtitles, her name is given as "Aerith" also.

Most of them are; Steve Burton and Christy Carlson Romano both play Cloud and Yuffie. Cid is not given a voice in KH1 but Chris Edgerley voices him in KH2. Also, Mandy Moore does not play Aerith in this, instead it's Mena Suvari who has the role in KH2. Lance Bass does voice Sephiroth, it's George Newbern (a.k.a. Nooj in X-2). Rachel Leigh Cook plays Tifa in this and KH2.