"A" is for Anya. :)
"A" is also for 'arc', a story that plays out over several episodes. A traditional story has a beginning, middle, and end. Are arcs then the province of guest characters?
Consider Parker. He's introduced very early on in 4th season. Seduces Buffy in The Harsh Light of Day, gets bapped by Buffy in Beer Bad and punched by Riley in, I believe,The Initiative - then he's gone.
Then there's Veruca. She first appears in Living Conditions, next seen in Beer Bad, leads Oz astray in Wild at Heart and later dies in the same episode.
Wait! These arcs are not about Parker and Veruca, but about Buffy and Oz/Willow respectively. So while an arc has a beginning-middle-end, its story doesn't have to end a character's story. In a show where a character can develop1, an arc serves as a stage for such a development.
"S" is for story, "P" is for plot, and "N" is for narrative. How do they relate?
- The story is what happens.
- The plot is why and how it happened.
- The narrative is how the story and plot are arranged to tell. A simple example ...
The Uber-Vamp stabs Buffy in the back and she collapses on her face.
Seven Years Earlier
INT. SUNNYDALE HIGH
Darla tells the boy she's scared to go into the high school in the dark.
Fortunately, this narrative was not contemplated. *g*
"B" is for 'The Buffy", said to be Joss' term for the thing in an episode causing the pain - and the learning or growth. In Lie to Me Ford's betrayal might be called the episode's "Buffy", but it's more likely it was the brain cancer which motivated Ford to betray her. Wanting to betray her simply for immortality is wanting something beyond what humans can normally demand. Who wouldn't want to avoid such a death? Buffy and Giles say it better in the final scene.
"B" is also for "Backstory". Yes, we all know Buffy's and Angel's and Spike's ... but what of Faith's? Don't say you know her backstory - sure she told us in Faith, Hope, and Trick and bits and pieces to the Mayor and there was that trade book .... But that's not her real backstory. Seriously, it's not. *g*
1 "C" is for "Character". In the beginning of a serial story it seems writers often times depend on cliche and stereotype for secondary characters because it makes the story easier for everyone. However, if you keep a character on stage long, you probably will do well to develop her character. Thus, Cordelia becomes Cordy.
Letters down: A, B, C, N, P, and S (which is also for 'Spike', but what's to say about Spike? Oh, another example of character development driven by audience reaction and story need).