Juhani is a Cathar female Jedi pupil on Dantooine. Shortly before the player arrives on planet in KOTOR, she attacks her master in a fit of rage, and believing her dead, and herself lost to the darkside, flees to a grove a short distance away from the academy. There, her Force-enhanced rage corrupted the local animals, and killed any people who dared to enter her grove. The player, upon completing their Jedi trials at the academy, was given the final task of "purifying" the grove. After entering the area, the player's party was immobilized by Juhani, and they entered a one-on-one duel. When she was near being defeated, Juhani would stop to talk. Here, the player could learn about what had happened to her, and convince her to return to the academy, or the player had the chance to kill Juhani.
If the player does kill Juhani on Dantooine, later in the game, on Korriban, you will encounter Juhani's friend, Belaya, who, stricken by the grief of her friends death, has turned to the Dark Side and joined the Sith. She will attack the player character, and try to kill you in vengeance.
If the player did not kill Juhani, she would become a party member and assist in the search for the Star Forge. Juhani is a Jedi Guardian class, meaning her focus was on combat with a lightsaber, not the Force or other abilities. If the player, regardless of gender, explores a relationship with Juhani, it is eventually revealed that Juhani has romantic feelings for the player character. This relationship is not explored past Juhani's declaration of her love. This is because it was originally intended that Juhani would be a lesbian, and only be attracted to female players. In the final product, however, Juhani appears to be bisexual, and will declare her feelings for both male and female PCs. If the player decides to side with a dark side-corrupted Bastilla on top of the Temple of the Ancients, Juhani will turn on you and attempt to kill you, along with Jolee Bindo.