Joy was one of the five Force Priestesses who, after their deaths, managed to keep their consciousness intact within the Force and resided within the Wellspring of Life. She appeared as a figure clad in a black robe, wearing a mask that radiated cheerfulness, and behaved in a way that reflected the emotional aspect she personified. When Jedi Grand Master Yoda journeyed to the planet in search of immortality, she and her fellow priestesses presented him with a series of trials to determine if he was deserving of the "great gift". Yoda successfully completed each of their challenges, ultimately venturing to the Sith homeworld of Moraband, where his final test—a confrontation with Sith Lords Darth Sidious and Count Dooku—was beyond the control of Joy and the other priestesses. After Yoda's success, the priestesses informed him that the spirit of his deceased friend Qui-Gon Jinn would communicate with him to impart the knowledge of how to manifest in the Force after death.
Joy was among the five Force Priestess who, even after death, could manifest in the Force, existing in a state between realms. Within the Wellspring of Life, located at the heart of the galaxy, she and the other priestesses—Serenity, Sadness, Anger, and Confusion—watched over all beings strong in the Force from their home.
During the Clone Wars, a conflict between the Galactic Republic and the Confederacy of Independent Systems, Jedi Grand Master Yoda sought out the Force planet. He hoped to learn how to overcome death, following the advice of his late friend Qui-Gon Jinn, who had also manifested in the Force after his passing. Serenity was the first to greet the Grand Master, notifying him that he was tardy and that the priestesses had been waiting. She guided Yoda to a gathering room where the other priestesses appeared around him. Each priestess responded to Yoda in a way that matched the emotion they embodied, with Joy expressing her belief that the Grand Master possessed the ability to successfully learn how to sustain his consciousness after death. Serenity then requested the blessing of the other priestesses, and the five joined hands, beginning a rapid spin around Yoda that blurred into a blinding light, transporting him elsewhere on the planet, where Serenity would begin his trials.
The Grand Master successfully completed his initial trial by conquering his fears. Following this, Joy and the other priestesses manifested behind Serenity as she stated that Yoda needed to trust in their teachings to succeed. The priestesses then instructed him to traverse the Valley of Extinction, warning him that he must do so without emotion, or he would see their faces and be tempted. Yoda successfully resisted temptation and reached the other side of the valley. There, Joy, Anger, Sadness, and Confusion established his final trial: a journey to the Sith homeworld of Moraband to confront his greatest fears. Once their challenge was set, they dematerialized, causing their robes and masks to fall to the ground.
On Moraband, Yoda encountered the specter of the Sith Lord Darth Bane, who attempted to lure him to the Dark side, but failed. Joy and the other priestesses then manifested before Yoda, cautioning him that while all his previous trials had been created by them, the final test was beyond their control. Yoda was to enter a chamber of darkness where the Sith once sacrificed Jedi, and where he would have to face the Sith of his era, Darth Sidious and Count Dooku. The five then faded away, leaving the Grand Master alone for his final challenge. Yoda faced the Sith and emerged from the chamber, where Serenity informed him that Jinn would commune with him and train him to achieve immortality.
Joy, along with the other four priestesses, who called each other cousins, represented the connection between the Living Force present in living beings and the broader Cosmic Force. While her form was adaptable, she generally appeared as a gray-skinned being, embodying the emotion of joy, with yellow eyes. Her manifestation included a black robe and a white, smiling mask.
When interacting with Yoda, Joy acted in a cheerful manner, fitting the aspect she represented. After Serenity presented Yoda to the priestesses, Joy was delighted to see him, stating that he was full of the Force and telling Anger that it was nonsense that the Jedi should not of been brought before them. She was confident that Yoda would succeed in learning to manifest in the Force after death, but still laughed when Anger pointed out that he should not be scared as he did not know what it was he had to face.
Joy and the other Force Priestesses were conceived for Destiny and Sacrifice, a pair of episodes from the sixth season of Star Wars: The Clone Wars. After the two episodes were completed but before their broadcast, the television series was canceled. Nevertheless, all of the episodes completed for the sixth season were released in 2014 under the title The Clone Wars: The Lost Missions on Netflix.
Jaime King provided the voice for Joy, as well as the other priestesses, recording the dialogue while switching between all five voices, with the exception of some specific sound clips like laughs. Dave Filoni, the director of the Clone Wars series, stated in a Q&A session on the Lost Missions that he envisioned the five Force Priestesses as a single being who had died and become a Force ghost, splitting over time and existing in the Force with a limited ability to manifest themselves. He also mentioned that the priestesses did not operate within the framework of good or evil.