Character background
Billie Jenkins is introduced in the show's eighth season as a young witch who pays more attention to demon fighting than to her education. At first she is introduced as a new charge for Paige Matthews, much to Paige's annoyance as this is at the time when the Charmed Ones want to remain hidden. However her character is quickly established as a powerful witch who at first does not really want any help.
When Billie discovers Paige's secret, that she is a Charmed One, she quickly persuades the sisters to teach her everything they know about witchcraft in return for keeping their identities secret. This agreement works both ways, Billie keeps their secret while learning about her craft and carrying out magic-related tasks for the sisters.
Billie's back story involves the abduction of her sister, Christy Jenkins, by mysterious demons with unknown intentions. This is Billie's main motivation for her constant training. Her main objective is to find out who kidnapped Christy and to save her if she is still alive while investigating why it happened in the first place. . Upon meeting with an Angel of Destiny, Billie is assured that her sister is alive and she will eventually find her. As the season progresses, her sister is revealed to have been kidnapped by the Triad, a trio of upper-class demons thought dead, because she is the key to the "Ultimate Power". This is revealed to be Billie herself, as stated by the Triad.
Billie is finally reunited with sister after 15 years. She starts to teach Christy in how to control her powers. When Christy is kidnapped by the demons that are sent by the Triad, Billie goes to rescue her sister, unwilling to lose her again. While they are both down in the Underworld, Billie persuades Christy to vanquish the demons. Together, with Christy's pyrokinesis power and Billie's telekinetic powers, they kill the demons - creating the Ultimate Power that had been foreseen by the Triad. What Billie doesn't realize is that Christy is working with the Triad, the same trio of demons who sent Cole Turner/Belthazor after the Charmed Ones. It is originally believed that they are the major threat the sisters are supposed to face. This is not the case, as Leo Wyatt, Piper Halliwell's husband, is not returned by the Angel of Destiny after two of them are vanquished. The remaining Triad member reminds Christy that Billie is the "Ultimate Power", and she must save her from the Charmed Ones, who have since been vilified. Through manipulating certain events, Christy manages this and Billie turns on the sisters, although she is reluctant to kill them.
Billie and Christy face the sisters in the manor with both sides empowered by the supernatural force called The Hollow. Because each side have taken in The Hollow and Billie and Christy having stolen Wyatt Halliwell's magic, their powers are evenly matched. The vast amount of power quickly spirals out of control, resulting in a massive explosion which obliterates the Manor and kills Phoebe, Paige, and Christy. Billie and Piper are the only survivors. After the battle The Hollow returns to its containment.
Following this destruction the Angel of Destiny brings back Leo, who stops Piper from killing Billie. While Piper attempts to find a solution with Leo, Billie returns to the Magic School and finds Dumain who attempts to trick her into warning the Triad of their destruction and realizes that she and her sister have been used. Using her power of projection, she projects herself back in time to try and prevent the recent events and to persuade her sister to stop trying to kill the Charmed Ones.
Through a series of events in which Leo and Piper travel through time to fix what happened, Billie goes directly to her past self and her sister, but they attack her, which would have allowed the events to carry on as normal if it wasn't for Piper who, with the the help of Patty and Penny, who had been recruited from different times in the past, banishes the Hollow before the explosion happens.
With these events changed, and all the witches now alive, Billie tries to reason with Christy, but quickly realizes she cannot be changed and returns to the Halliwell sisters. Using her powers to project herself and the Charmed Ones to the Triad before the any of the witches call for the Hollow, they find Dumain and Christy have also traveled back to warn them. This however does not stop the sisters from vanquishing the Triad along with both future and past Dumain. In an act of rage, Christy throws a fireball at Billie, who is forced to kill her in self-defense by telekinetically deflecting the fireball back at Christy. With her entire family gone (Carl and Helen had been murdered by demons sent by the Triad to turn Christy truly evil), she breaks down as the sisters show their remorse and comfort her.
In the final Charmed episode when the Charmed Ones start to write their story down, it is revealed that Billie remains a close family friend and the sisters' strongest ally. She is seen in the finale babysitting Phoebe's two oldest daughters. (Out of the three sisters, she was closest to Phoebe, because even though Paige was her Whitelighter, Phoebe was the one who was always there for Billie and always saw the best in her. Phoebe was also the Charmed One who most strongly protested killing Billie after the secret of the "Ultimate Power" was revealed.)
Though Billie and Christy were both witches, albeit ones that manifested their powers later in life than normal, their parents had no magical powers and were mortal. Both of their parents were the product of unions between a witch and a mortal, resulting in normal mortal children with latent witch genes. It is confirmed that Billie's grandmother was a witch.
Powers and abilities
Billie has the power of telekinesis, the ability to move objects with her mind. It is suggested that she learned to master her powers quickly as she used her telekinetic powers to enhance her natural acrobatic and fighting talents so that she could perform flips and other gravity defying manoeuvres. Billie told Paige she hadn't had her powers for "that long"; most likely being a year at the most. As she grew as a witch a second latent power manifested: the ability of projection. This power was initially identified as the ability (as Phoebe put it) to turn people and things into whatever comes to mind without a spell or potion, but was later revealed to be a greater power to manipulate reality and time itself.
At first the power activated subconsciously, while Billie was suppressing her emotions, transforming an object without her intention. She transformed fresh flowers into dead ones after saying her parents are going to "suck the life out of this place" and then the plants literally got the life sucked out of them. Then accusing her parents of being "cold hearted assassins", accidentally transformed them into just that. Upon gaining greater control over the power she displayed the ability to transform a dying Penjing tree into a younger, healthier version of itself at the 'beginning of its cycle', cleanse The Charmed Ones of evil influence, create illusionary duplicates of herself and her sister and also amplify Christy's power to the degree that it could incinerate a demon thought unvanquishable. Another powerful application of this power was to allow Billie to transport herself through time by force of will. Another power she demonstrated was Astral Projection although it's not known if it's just part of her Projection power or if it's another power she possesses, when demonstrated it looked similar to Prue's Astral Projection in the episode "Kill Billie Vol. 2".
