If you are reading this guide then you probably know that Aeris, unhappy wth Clouds leadership decides to take her equipment and leave the party.
She then has an accident and stumps her toe which as we all know, is extremely painful.

In order to show her the error of her ways and prevent that horrid toe stumping incident we need to prepare a few things which this guide covers.

It is impossible to recruit Aeris and do a 100% run! so keep that in mind.

It is also worth noting that their have been many, many guides in the past that have promised the ability to do this and it was universally believed to be impossible so I will be covering in detail why this works and also why it prevents a 100% run.

This is a check list of everything you need.

• Yuffie has not been recruited
  
• Cid has been recruited
  
• Dio has not offered the Keystone

The requirements are thankfully not that hard, which means you can speedrun to this point in the game. You can't 100% your savefile but you might want to pick up as many items as possible anyway since you will only be skipping 2 dungeons anyway but sadly the contents of those dungeons are important to completionists because Temple of the Ancients has both Morph and Bahamut which means no infinite sources and no Bahamut-Zero.

Yuffie is needed for Yuffie warping which I will explain in the next section.

Cid is not required however the Tiny Bronco will help a lot and you need it anyway to reach the Temple of the Anicents.

When Dio offers the Keystone a series of events playthrough that lock Aeris into the party. You can keep her locked into the party however their are times when this will crash the game!

Yuffie Warping is a glitch only on the PC releases of FF7.
At the time of writing it seems the PS4 re-release may use the PC release code which would enable Yuffie Warping on that version too but we will see.
Many guides over complicate this but its really easy to do.

Step 1.
Die in any non world map battle.
Simply put, anytime you are not on the world map you can die in order to warp. Their is a handful of exceptions but honestly just keep it simple and die indoors.

Step 2.
Do not exit the game! Load the save file that you wish to transfer.
This file must not have Yuffie recruited but for simplicity sake, just never recruit her at all.

Step 3.
Reach any forest and fight/run away until you fight "Mystery Ninja" and win.

That's it. Instead of the dialogue occouring when you would try to recruit her you will instead immediately warp to the point you died.

This glitch has various side effects to keep in mind. First of all the game will move the buggy and tiny bronco to where they were in the save file you transferred so while it is rare due to the proximity of everything on disk 1 it is very possible that you maybe unable to reach either vehicle! For this reason many guides say you should just get a gold chocobo and the highwind instead.

The second thing to keep in mind is that you must be outdoors on the save file you are transferring, if you ever enter a field map(indoors) the glitch will not work!
It is probabaly best to save near a forest anyway in preparation for the warp.

Yuffie warping is pretty crazy and has very few limitations, you can even warp back to the beginning of the game with a Lv99 Cloud and knights of the round the two shinra soldiers when you get off the train that said however their are times when the game will force you to have certain party members or you would not have access to other party members. At these times the game is very likely to crash so keep many seperate save files.

Once you know how to Yuffie Warp it becomes quite clear what you need to do in order to keep Aeris around but just to clarify I'll outline what you are doing and why you are doing it.

As soon as you talk to Dio/examine the keystone you cannot leave the gold saucer so while technically you can save after examing it but before the date, it is safer to just not bother and keep a save file from before you examine it. Keep this save file seperate.

Aeris demands to join your party for the Temple of the Ancients and she is deleted at this point. You can run the Temple of the Ancients but she will be locked into the party (because she is pending deletion) so if you tried to warp at this point you will always have her in your party as you can never take her out! Eventually this causes crashes.

You now need to continue on until the start of disk 2. You can warp her to the fight against Jenova-Life but if she is in your party when you kill the boss then the game will crash so it is safer to just skip it and start at disk 2 instead. Keep this save file seperate, too.

You can now get into any (indoor) fight and die. Load up your second save file that has Aeris alive and Yuffie Warp. The downside here is that you will not be able to do the Temple of the Ancients, thus missing various goodies.

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You will always have to skip the Temple of the Ancients to keep her and if you warp after disk 2, back to disk 1, then she will either be locked out on the PHS menu or she will be locked in depending on your actions which is a huge problem. You gain access to these via the huge materias so it isn't a huge loss but it is something to keep in mind.

With so many topics back in 1997 about ways to keep Aeris, it comes as no surprise that many people are skeptical or just denounce everything related to this as being nonsense.
This is not helped by this being exclusive to the PC version which has its share of mods, hacks and even cheat engine that can all place her into the party to make any 'method' seem legit, no matter how bogus it is.

The main thing to take away from this guide is Yuffie Warping. It doesn't take long to prove that Yuffie Warping works and that it can be used to jump around the game freely. Once you know how to successfully Yuffie Warp then regaining Aeris seems easy.

The problem is that she has special flags to remove her from the party and to lock her into the party and you need to avoid these flags because once they are on, you can't take them off without hacking/cheat engine and at that point it is faster to simply use those tools to re-add her.

This guide came about from a desire to legitimately add her to the party whilst doing a 100% run which lead to the discovery of the various issues she causes if you wait too late to warp. Orginally I was going to warp after the Temple of the Ancients in order to regain her but that causes the removed switch to activate so even if you add her back to the party, you can't use her!
I then loaded from earlier but because I had the keystone she was once again locked into the party. It seems that you must prevent her from being locked into the party at all or else you are out of luck.

Also you can warp forwards and backwards with the Yuffie Warp but the Temple of the Ancients will always lock Aeris into the party which is a problem but even outside of that their is another problem with the temple. Entering any of the doors inside the temple will freeze the camera! So even navigating the temple is a huge problem! It is far safer to simply run the temple on your main save file and then warp beyond it on your Aeris save file than it is to attempt the temple.

Another common problem that people experience is that they warp backwards and rescue Aeris but she is still locked out of the party! The reason for this is because the save file where you lose Aeris has her removal flag turned on and when you warp, you retain your savefile data. This means you can Warp Aeris forward because in her savefile her flags haven't been toggled yet however if you warp backwards (after she leaves) then the flags are now on. This means you cannot playthrough normally and then just warp back to the beginning of the game to collect her because as you discover, you can manage her materia but you cannot place her in the party.

As far as I know, you can only warp her forward in order to keep her as a regular party member. Every attempt I have made in the reverse direction has caused her to lock, so keep this in mind and keep multiple seperate save files!