Joss was very similar to Kim, in that she was perky, adventurous, and something of a tomboy. In addition, because Joss considered her own life boring, she was always eager for new adventures, and faced potential danger with excitement rather than fear.
Joss looks up to Kim and, for a time, Kim's exploits were a source of obsession for her. She knows every one of Kim's missions by heart. While Kim found it flattering at first, the novelty quickly began to wear thin.
Joss ultimately ended up saving Ron from Shego by deactivating her father's robot horse, "Ol' Tornado". Ironically, after seeing Ron in action, she began to find herself a new hero in him. Even though Ron has plenty of fear to go around, this fear has never stopped him from helping Kim. This began to show Joss how a person can succeed when being herself and that she did not have to transform herself into someone else to be better. But before when Kim told that she was being 'me' to save the world, she never cared. In the end, she chooses Ron as her role model. From this we understand she can be anyone but herself.
Joss is very slim, and about a head taller than her cousins Jim and Tim. She resembles Kim quite a bit, except for being shorter, having a tanned skin and having freckles, which Kim also had when younger.
Joss displayed a love for adventure that rivaled Kim's own. As a result, Joss was virtually fearless in dangerous situations, and all too eager to prove herself to Kim. Having lived on a farm with robot horses, Joss also had a level of familiarity with cybertronics that Kim admitted she herself lacked.
Little is known about Joss or her history. She is Kim's cousin and the daughter of Slim Possible. She made her first and only in person appearance part was through Season 3, and was introduced when the Possible Family and Ron visited her family's ranch during summer vacation in the episode "Showdown at the Crooked D". She appears to be the same age as the tweebs.
During this episode, Joss and Slim helped the other members of the Possible family in foiling a scheme by Dr. Drakken to transform the world's geniuses into lackwits using brain wave altering cowboy hats, before learning that she needed to follow her own path in life.
Two separate pictures of Joss were visible in the family photo wall scene during the Season 3 finale.
- Joss is notable within the franchise in that she and Kim's mother, Dr. Ann Possible are the only characters who have been specifically confirmed as a Possible who goes by a name which is not an allusion to the word "impossible"; it was never stated whether Cousin Larry was a Possible. However it could just be an allusion to "just (barely) possible", as in she is "just barely like Kim".
- For some some undisclosed reason, Joss was not with her father at Kim's graduation.
- The episode in which Joss appears originally went straight to video in the US before hitting the airwaves.
- Even though Kim gets most of her looks from her mother, Joss looks more like she could be Kim's younger sister.
- In "October 31st", there was a girl Trick-or-Treater in a bunny suit who looked like Joss and was also voiced by Tara Strong. Even her addressing Ron as "mister" does not threaten a continuity error as Joss initially could not remember Ron beyond wearing the pants whose pocket Rufus lives in and as "the one who's always losin' his drawers".
- Joss is Kim's biggest "fan."