Little is known about Faith's earlier life. Her dialect and early exposition suggests she grew up in the notably rough neighborhoods of South Boston. Her father is never mentioned. She makes several references to her mother's alcoholism and possible allusions to childhood abuse. ("My dead mother hits harder than that!" — "Faith, Hope & Trick"; she mentions her mother in a torture scene in "Five By Five"). She also clearly suffers from trauma and abandonment complexes resulting from the murder of her Watcher by a powerful ancient vampire. Early on, Faith harbored envy toward Buffy ("Enemies") for having a loving relationship with her mother and friends, the same one she had always wanted. Jealousy later changed into self-hatred as she realized the power and accountability she has over her own life. By Season 7, self-hatred had faded into self-acceptance; she had learned to accept the consequences of her past actions. Faith often suggests that killing gives her a drug-like euphoria, and even suffers from addictive withdrawal symptoms when she is not able to inflict pain. In the Angel episode "Sanctuary", quitting violence is equated with quitting alcohol (Faith: "I gotta be the only Slayer in history to be sponsored by a vampire.") She is seen smoking in Buffy's season 7.
Faith also displays signs of promiscuity and an inability to share trust and intimacy with a man, describing herself as "a loser magnet" who attracts men like kleptomaniacs and "slackers". Faith was later responsible for Xander Harris losing his virginity and sleeps with Buffy's boyfriend Riley Finn in a later season, after switching bodies with Buffy herself.
It is unknown when Faith was contacted and began training with her Watcher, though she appears to have been recruited as a teenager like Buffy (rather than as a child, which is considered ideal for a Slayer.) It is also unclear how long Faith had lived on her own before coming to Sunnydale.
Sunnydale
When Faith first arrives in Sunnydale ("Faith, Hope & Trick"), she has been traumatized by helplessly watching the vampire Kakistos gruesomely murder her Watcher, explaining to Buffy that "they don't have a word for what he did to her." She has run away from trouble since childhood, but begins dealing with those issues after staking Kakistos. Faith feels like an outsider in Buffy's world even though she initially endears herself to Buffy's mother and friends. Buffy, who is still recovering from the trauma of killing Angel, maintains emotional distance from Faith and withholds Angel's return from her ("Revelations"). Although Buffy resents Faith's carefree attitude toward violence, she still trusts Faith enough to leave her to protect her mother at Christmas ("Amends") and even shows hints of being attracted by Faith's wilder way of slaying ("Bad Girls"). Faith perceives that Buffy does not trust her, further alienating the two. Faith's isolation heightens when her new Watcher, Gwendolyn Post, abuses her trust to plot an evil scheme. She then accidentally kills the Deputy Mayor, Allan Finch ("Bad Girls") and goes into denial. When it becomes clear that Buffy intends to confess, she tells Giles that Buffy had killed Finch. Giles plays along to avoid pushing her too far. The Scooby Gang decides to help Faith. Xander visits Faith's motel room to reason with her, but she nearly strangles him instead. Angel arrives in time and takes her to his mansion and tries to reason with her.
Meanwhile, Buffy's new watcher, Wesley Wyndam-Pryce, hears of her crime and tries to arrest Faith with the help of a group of Council Operatives. Faith attacks them in the armored car and escapes ("Consequences"). Isolated and bitter, she secretly turns to Mayor Wilkins, the major antogonist of the third season, filling the void of Wilkins' "right hand man" left by the vampire Mr. Trick, who Faith has recently dusted. Faith and the Mayor develop an affectionate, emotional closeness, and she comes to see him as a father-figure. While serving the Mayor undercover, she kills a smuggler and a bookseller demon. She kidnaps Willow Rosenberg at knife-point and wants to kill her ("Choices"). She also kills a professor without question. Her duplicity is exposed when she tries to rob Angel of his soul ("Enemies"). Despite her actions, Faith is somewhat surprised when Willow tells her that she is beyond help ("Choices").
Faith then shoots Angel with a poisoned arrow, deliberately missing his heart. The only antidote is draining the blood of a Slayer. Buffy visits Faith's apartment to kill her, intending to sacrifice Faith to save Angel, but Buffy only manages to stab Faith in the gut with her own knife, a gift from the Mayor. Faith jumps from the apartment building roof onto a moving truck and escapes ("Graduation Day, Part One").
Faith is brought to Sunnydale hospital in a coma. While Buffy lays unconscious nearby (having been drained by Angel), they share a psychic dream where a pleasant Faith told Buffy that the Mayor's human weakness will never go away ("Graduation Day, Part Two"). Later, while Faith is still in her coma ("This Year's Girl"), she dreams of Buffy; Faith still has the knife in her abdomen (from the end of the previous season) and asks Buffy if she was ever going to remove it. She is also pulled into Buffy's dreams, revealing that she is still unsure about Buffy's feelings.
After the coma
Faith awakes in the middle of Season 4 ("This Year's Girl"). She learns what has happened while she was gone, gravely injures the girl who tells her, and surprises Buffy on the college campus. Faith is angry at Buffy's attempt to sacrifice her for Angel ("You tried to gut me, Blondie"), and devastated about the death of the Mayor. After a fight, Faith escapes from the approaching police and later attacks Joyce, Buffy's mother, at her house. As Buffy is about to win the ensuing battle, Faith uses a magical device, a gift from the Mayor, to swap bodies with Buffy. Buffy, in Faith's body, is kidnapped by the Watchers' Council's Special Ops team to be taken to England, while Faith (as Buffy) plans to flee the country. Tara Maclay realizes something was wrong and tells Willow. Faith sleeps with Buffy's boyfriend, Riley ("Who Are You") and flirts with Spike. She eventually begins to understand Buffy, however, and savagely beats herself in self-hatred. With Tara's help, Buffy manages to undo the body switch and Faith leaves Sunnydale like a fugitive on a freight train.
In Los Angeles, she rampages through the underworld, stealing and squatting in her victims' apartments. She is approached by Wolfram & Hart, who have learned that a "rogue Slayer" was in town, about killing Angel. She shows Angel her "evil" by kidnapping Wesley and brutally torturing him, but in a fight with Angel, she begs Angel to kill her. Angel refuses and begins the task of saving Faith's soul, forgiving her and working to break down her emotional walls. Just as Faith begins to feel remorse for her crimes, Buffy shows up looking for revenge, insisting that Faith must go to jail. In the meantime, the Watchers Council also shows up, intending to kill Faith. Faith decided to surrender to the police and face the consequences for her actions. She is sentenced to a women's prison, where Angel checks up on her regularly. Faith, ironically, finds some level of stability in her prison life, noting that at least she had three meals a day and a place to sleep. Although capable of escaping at any time, Faith chooses to cooperate with the terms of her confinement.
In Season 4 of Angel, Faith is attacked by a Bringer's knife in prison; although Buffy and the Scooby Gang in Sunnydale are aware of the threat posed by the Bringers, they fail to warn Faith of the danger. Soon after, she is recruited by Wesley to help find a soulless Angelus and assist in restoring his soul yet again. Without hesitation, she breaks out of prison. She battles Angelus and uses a mystical drug to infiltrate his mind while Willow works a spell to restore his soul.
After Angel's re-ensoulment, Faith travels with Willow to Sunnydale to battle the First Evil. She initially follows Buffy's command ("Dirty Girls") even though she has some doubts about Buffy's decisionmaking ("I'm with you, drop me in the hornet's nest, what the hell"). Buffy is less than enthusiastic at Faith's return, but realizes that reinforcements are desperately needed. However, when Buffy loses the confidence of the group and is kicked out of the house, the Potentials turn to Faith for leadership. She reluctantly agrees to lead, ("Empty Places"), but her first attack leads the potential Slayers into a trap ("Touched"). Faith is badly wounded but is saved by Buffy and the surviving Potentials. When the Potentials complain about Faith's decision, Buffy defends her, and she and Buffy finally make peace ("End of Days"), noting that the friction in their relationship is perhaps due to the fact that under normal circumstances, two Slayers are never supposed to live at the same time. Faith plays a pivotal role in the final battle with the First Evil's army ("Chosen"), 'holding the line' after Buffy is stabbed by one of the Turok-hans.
