THIS ACTUALLY WORKS, and it doesn't involve getting 99 tissues or beating the game fifty times in one day! Unfortunetly, this can only be done on the PC version of FFVII. If you know nothing about computers besides how to play FF7, see below. If you know how to handle a computer, just skip to the overview.
First you'll need to download a program called mtrainer. Download it from here. It's a form of cheating device for the game, and has many good features, but you don't have to use them if you don't want to. Don't worry, many people (myslef included) have tested it, and it won't harm your game or comp in any way. Unzip the program and make a copy of its folder (right click on the folder icon and copy, than paste it somewhere else) in order to get to it again without unzipping. After downloading the program, open FF7 and load the save file you want Aeris or any other cheat on. While playing, minimize the game (so you can get to and open the program) and open the mtrainer folder (from wherever you saved it to). Open the program (not the notepad, this has a different, greenish icon) labled ff7bstrn. Once the program is open, simply click on "bring back all allies" towards the bottom. Restore the game to full size and look at the PHS (party select) menu. Aeris should be available, with the same level and stats she had before. NOTE: The notepad labled ff7bstrn gives more instructions on using the program's other features.
This is all much faster and less complicated than it sounds, I just tried to make it easy to follow for both veterans and computer newbies.
Here is an overview:
1. Download mtrainer
2. Open FF7 and the save file of your choice.
3. Minimize the game
4. Open FF7BSTRN (the program) and click on "bring back all allies"
5. "Operation complete" should be displayed.
6. Aeris should now be in your PHS menu. You don't have to keep mtrainer open anymore.
7. Save your game in a different save slot (to be safe)
8. Use whatever other cheats you want on mtrainer at your leisure.
Don't do this in Midgar, unless you want to be invisible when you enter towns or caves. I did it on the Highwind, and so far there haven't been any glitches. I also recommend doing this on a copy of your save file, in case any gltiches I'm unaware of occur.
Although Aeris is not "officially" back in the story, she does speak, fight in battles, and appear onscreen like a normal character. She also appears in cutscenes sometimes (dialogue, not FMVs). She even has some unique situations which wouldn't be possible if she was considered not to be there. Tell me if you encounter any unique situations concerning Aeris.
Please submit any secrets you would like to see on this site.