<P> "Once More, with Feeling" explores changes in the relationships of the main characters, using the plot device that a demon--credited as "Sweet" but unnamed in the episode--compels the people of Sunnydale to break into song at random moments to express hidden truths . The title of the episode comes from a line sung by Sweet; once the characters have revealed their truths and face the consequences of hearing each other's secrets, he challenges them to "say you're happy now, once more, with feeling". </P> <P> All of the regular cast performed their own vocals, although two actors were given minimal singing at their request . "Once More, with Feeling" is the most technically complex episode in the series, as extra voice and dance training for the cast was interspersed with the production of four other Buffy episodes . It was Joss Whedon's first attempt at writing music, and different styles--from 1950s sitcom theme music to rock opera--express the characters' secrets in specific ways . The episode was well received critically upon airing, specifically for containing the humor and wit to which fans had become accustomed . The musical format allowed characters to stay true to their natures while they struggled to overcome deceit and miscommunication, fitting with the sixth season's themes of growing up and facing adult responsibilities . It is considered one of the most effective and popular episodes of the series, and--prior to a financial dispute in 2007--was shown in theaters with the audience invited to sing along . </P> <P> Throughout the series Buffy Summers (Sarah Michelle Gellar), in her role as the Vampire Slayer, is assisted by her close friends, who refer to themselves as the "Scooby Gang". These include Xander Harris (Nicholas Brendon), a young man without particular strengths or talents, but devoted to Buffy and her calling, and Willow Rosenberg (Alyson Hannigan), a young woman who has grown from a shy but gifted student into a strong woman and powerful user of magic . They are mentored by Buffy's "Watcher", Rupert Giles (Anthony Stewart Head), a paternal figure since the first season, when Buffy moved to Sunnydale after her parents' divorce . Xander is engaged to Anya Jenkins (Emma Caulfield), a former vengeance demon who has become human . They have struggled with disclosing their engagement to the rest of the group and individually doubt their impending marriage . </P> <P> Buffy died at the end of the fifth season ("The Gift"), sacrificing herself in place of her younger sister Dawn (Michelle Trachtenberg) in order to save the world . In the first episode of the sixth season, Willow, believing Buffy to be in Hell, used magic to bring her back from the grave . Buffy was in fact at peace, in what she thinks was heaven, but she has kept this a secret from her friends . Since her resurrection, Buffy has been lost and without inspiration to perform her duties as a Slayer . Willow is romantically involved with Tara Maclay (Amber Benson), a powerful but ethical witch . Tara has previously expressed concern at Willow's use of her emergent magical powers for trivial or personal matters . In the preceding episode ("All the Way"), Willow cast a spell to make Tara forget an argument about her abuse of magic . In the same episode, Dawn, who has been stealing from stores, including Anya's magic shop, lies to Buffy and goes on a clandestine and almost deadly date . Left to take care of Dawn after the death of their mother Joyce Summers (Kristine Sutherland) in the fifth season ("The Body"), Buffy has come to depend more heavily on Giles . Following Dawn's date, Buffy asks Giles to shoulder responsibility for disciplining her, much to his discomfort . </P>

Who played the demon in buffy once more with feeling