Selfless

In which Anya turns her back on vengeance and it bites her in the ass. Which, really, you'd except vengeance to do.

Official back-of-box synopsis:

When Anya summons forth a giant spider demon to kill a large group of fraternity brothers, Buffy realises she must kill Anya before she strikes again.

Cross-reference:

episodes in which we learn the origin of major characters:

• Becoming (part 1)
  Liam meets Darla in an alley in Galway
• Fool For Love
  The true story of Spike, not the one he tells
• this episode
  Anya, the early years

Cast:

• Sarah Michelle Gellar as Buffy
• Alyson Hannigan as Willow
• Nicholas Brendon as Xander
  

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• James Marsters as Spike
• Emma Caulfield as Anya
• Andy Umberger as D'Hoffryn
• Michelle Trachtenberg as Dawn
• Kali Rocha as Halfrek
• Abraham Benrubi as Olaf
• Jennifer Shon as Rachel
• Joyce Guy as Professor
• Taylor Sutherland as Villager #1
• Marybeth Scherr as Villager #2
• Allesandro Mastrobuono as Villager #3
• Daniel Spanton as Viking #1
• John Timmons as Viking #2