Location / Finding Yuffie

To recruit Yuffie, you must first find her; she lurks in any forest area in the game.

The earliest time you can enlist her to your party is when you have left the Mythril Mines, inside the forest on the way to Junon.

If you miss that location, do not worry. You can still recruit her in any forest (big areas of green plants and marsh on the world map) throughout the game.

Recruit Yuffie

Once in a forest, walk around and fight random battles until a thieving ninja girl eventually pop ups. This is Yuffie. You must defeat her in battle; it is ridiculously simple so do not fret. Be adequately prepared and completely ready for fire-based attacks and you should have no worries.

She appears as "Mystery Ninja" in battle, but will eventually reveal her real name, Yuffie Kirasagi, once she joins your party. Just keep attacking Yuffie while healing once in a while when you sustain enough damage and the battle should run by smoothly

After you have defeated her, you will automatically be taken to a small area with a save point with your three battling characters, and Yuffie lying on the ground. If you try to use the save point, Yuffie steals 200 Gil from you and runs away. So while here, do not save, but talk to Yuffie on the ground instead. She instigates and issues a challenge to fight you once again so she can prove herself. A conversation will take place and you must answer them correctly to get her your join your party.

Conversation

Yuffie: "You spikey-haireded jerk! One more time, let's go one more time!"

Response: "Not interested."

Yuffie: "You're pretty scared of me, huh?"

Response: "...petrified."

Yuffie: "I'm really gonna leave. REALLY!"

Response: "Wait a second!";

Yuffie: "You want me to go with you?"

Response: "...That's right.";

Yuffie: "All right! I'll go with you!"

Response: "...Let's hurry on."

After correctly responding to Yuffie's remarks, she will join your party. Congratulations!