<P> After years of foreshadowing, Dawn was introduced at the start of the fifth season as part of a large in - story retcon: Characters accepted Dawn's presence as if she had always been there, and as if Buffy always had a sister, with only the audience aware that this was not the case . As the series went on, the significance of Dawn's arrival is revealed to the series's other characters, and they come to understand that she has not always been Buffy's sister, or indeed a sentient being; Dawn had originally been the mystical "key" to unlocking dimensions and was made into Buffy's sister so the Slayer would protect her . Dawn is, however, a real girl, Buffy's biological sister, and has real memories of her fictional childhood . She struggles in a very human way when she discovers the truth about her origins and later endures problems with self - harm and kleptomania . The show's sixth and seventh seasons, as well as its canonical comic book continuation, follow Dawn's journey toward adulthood . </P> <P> Dawn was included in TV Guide's list of Most Loathed TV Characters . Similarly, Entertainment Weekly named her one of the "21 Most Annoying TV Characters Ever". </P> <P> Dawn is first introduced as Buffy's (Sarah Michelle Gellar) younger sister at the end of Buffy season five premiere "Buffy vs. Dracula", though Buffy had been previously established as an only child . Initially, the mystery of Dawn's sudden existence is not acknowledged in the series, with the other characters accepting her as a part of the status quo . Four episodes later Buffy discovers Dawn is in fact a mystical object known as The Key; a group of monks transformed The Key into human form and sent it to the Slayer for protection from the villainous Glory (Clare Kramer). The memories of Buffy and her associates were altered, along with relevant records, so that they believed her to have always existed as Buffy's sister . She is shown to look up greatly to Willow and Tara and has a crush on Xander . She also is friendly with Spike, who is as protective of her as Buffy herself . When Dawn learns of her origin, she resorts to self - harm and runs away from home, until Buffy assures her they are real sisters no matter what, securing it with a blood oath . Her relationship with Buffy, having been portrayed with a typical sister dynamic in the first half of the season, changes when she discovers what she is . The two become closer as Dawn becomes Buffy's sole focus once she drops out from college to protect her, going as far as to warn her friends she is prepared to kill anyone who attempts to go near Dawn in the finale . Dawn suffers more pain when her mother (Kristine Sutherland) dies unexpectedly from a brain aneurysm, which leads to Dawn resorting to black magic to try to bring her back from the grave, an action she immediately reverses upon realizing the consequences of her actions . It is eventually revealed that Dawn's purpose as The Key is to open portals to alternate dimensions, a power the hell - god Glory wishes to exploit to return home . When Glory successfully uses Dawn's blood to break down the dimensional barriers, Buffy sacrifices her own life, realizing that their blood is now the same, to end the apocalypse and save Dawn . Buffy's sacrifice also neutralizes the power of The Key, giving Dawn the opportunity of a normal life . </P> <P> The following season opening sees Dawn struggle with abandonment issues, as well as her escalating kleptomania . Having been devastated by her sister's death, Dawn is overjoyed when Willow (Alyson Hannigan) casts a spell to bring her back to life . However, with Buffy spiralling into a deep depression, Dawn feels highly neglected and is often seen alone and seeking attention from her sister as well as other members of the group . She later experiences her first kiss with a vampire named Justin, whom she is reluctantly forced to stake (her first vampire kill) when he tries to turn her . Dawn's isolation from the other characters reaches its apex when she inadvertently makes a wish to the vengeance demon Halfrek (Kali Rocha) which results in trapping everyone who enters the Summers house . Halfrek herself is inadvertently trapped, and undoes the curse to free herself; meanwhile Dawn's kleptomania and feelings of neglect by her friends and family are exposed . Buffy vows to mend their relationship and starts spending more time with her sister, whilst still trying to shield her from her life as a Slayer--much to Dawn's disappointment as she is eager to help Buffy in her duties . While helping Buffy battle demons in the season finale, Dawn proves herself to be capable in a fight, finally earning her sister's respect and a promise to train her . </P>

Where did buffy's sister come from in season 5
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