Superstar

In which we discover that the answer to life, the universe, and everything is Jonathan. He's so dreamy.

Official back-of-box synopsis:

Buffy uncovers why the whole town thinks that former high school nerd, Jonathan is Sunnydale's newest version of a superhero.

From the old WB Buffy website:

FANTASY VS. REALITY - Buffy, still reeling from the discovery that Riley was intimate with Faith, must put aside her personal emotions and summon the strength to uncover why the entire town thinks that former high school nerd, Jonathan, is Sunnydale's newest version of a superhero.

Cross-reference:

episodes featuring alternative realities:

• The Wish
  Sunnydale sans Buffy? Be careful what you wish for...
• Normal Again
  is the entire 'verse just insane-Buffy's hallucination?
• this episode
  where Jonathan is Keanu, Michael Jordan and Al Gore all rolled into one

episodes featuring dairy products:

• Never Kill A Boy On The First Date
  String Cheese is served in the cafeteria.
• Enemies
  The mayor pours Faith a glass of milk. She doesn't drink it.
• Living Conditions
  Kathy and Buffy argue over milk. Sid The Wiley Dairy Gnome is accused.
• Restless
  The Cheese Man wears the cheese, it does not wear him.
• Once More, With Feeling
  Anya's accused of eating skeezy cheeses
• Wrecked
  Willow mentions keeping "stinky yak cheese in my bra"
• Storyteller
  The Cheese Man makes a brief flashback appearance.
• this episode
  Anya needs help opening a milk carton. Xander's not man enough.

episodes with one-off credit sequences:

• The Gift
  images from all 99 previous shows
• Once More, With Feeling
  Musical-style "overture" credits
• this episode
  Jonathan-centric credits

Cast:

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

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• Anthony Stewart Head as Giles
• James Marsters as Spike
• Danny Strong as Jonathan
• Marc Blucas as Riley
• Bailey Chase as Graham
• Amber Benson as Tara
• George Hertzberg as Adam
• Robert Patrick Benedict as Jape
• John Saint Ryan as Colonel Haviland
• Erica Luttrell as Karen
• Adam Clark as Cop
• Chanie Costello as Inga
• Julie Costello as Ilsa