Secrets in 'Final Fantasy VII' come in many different shapes and forms, from Materia to super-bosses, there are even secret/hidden characters to find. One such character is the mysterious Yuffie Kisaragi. Originally from the village of Wutai, Yuffie is found far from home and all on her own until meeting up with Cloud and his friends.
Yuffie can be encountered at any point after the Mythril Cave, as a random battle in any forest on the world map. After the party defeats her, the party will be placed in an area appearing to be a generic field with a save point, and Yuffie will be standing, waiting to be talked to. The correct thing to do is to talk to Yuffie Kisaragi and answer each of her questions accordingly. If at any point the player picks a wrong answer, Yuffie will steal some of the party's Gil and run off. She will do the same if the player accesses the menu at any point, even to save.
Yuffie, once recruited, is seen as a mysterious thief/ninja type character, initially equipped with the Steal Materia upon recruitment. Her village, Wutai, which lies in the far north-west of the world on a narrow island, also includes two side-quests that will only occur if Yuffie has been recruited. The first of which can be done immediately following after in Rocket Town in disk 1. Disembarking on the island Wutai resides, and beginning to head for the village will cause Yuffie to stop everyone before being assaulted by Shinra troops. Miss Kisaragi will then become spooked and steal the entire party's Materia, and run off to her village where the side-quest begins.The second side-quest is simply Yuffie fighting through the five levels of her father's Pagoda, with a nice reward upon completing the entire trial.