When I first put up my blog, I spent a lot of time looking for things that made me happy. Writing, food, screenwriting, candy--random stuff because, hey--I'm easily bored.
UNK's fourteen part series on the transformational character arc, and Joshua James work on "non" transformational characters helped a lot.
In the beginning when I set up Dead Gorgeous, I had a lot of issues. For some reason the plot kept falling through. Connor was static because I mistook minor external conflict and the needs of my plot for his arc. Jacey was boring because while she had back story, she was cardboard too.
A love story, or any other kind of story where people connect is a story where side by side arcs move toward a common goal. Jacey and Connor both change. I kept thinking, okay--this is who they are at the beginning, this is who they are at the end....uhm?
Which is pretty much a plain English explanation of arc. They're something different at each point which means change happens over the course of the story. And to show change,the character must be distinctly different at each point. Not polar opposite different, but a marked change that is noticeable to your reader.
A good example would be Zarek in Kenyon's Dance with the Devil. In the beginning you see how life experiences and family have shaped Zarek into someone with so much rage he's just a ball of walking mad. The only way to tell there is something "more" is through his visible actions, because he refuses to admit he might still have feelings. He's kind to animals, he's kind to people in an offhand way if nobody notices, but if you confront him about it, he'd probably kill you without a second thought. He's lonely and disconnected. By the end of his character arc, he changes on the inside--but, on the outside, to people in other povs--he hasn't. We see him because we're the reader, so does Astrid--because she's the heroine, but to everyone else, he's still the same.
Which means transformation can be internal, and not visible to people outside the story, and can happen "through" interactions with a static character.
Astrid has no arc. She's who she is at the beginning and who she is at the end. Sure, she has a few issues dealing with external plot, and Kenyon gives her a little angst over her lack of emotion, but it disappears so fast, you know it's just window dressing. She doesn't change. She's the catalyst, and a pov character, but despite being a pov character with a stake in the story, her role despite being fifty percent of the book--is minor compared to Zarek's. Zarek is the hero of the story because he changes, and in a character driven story, the person with the most change is the person the book is about.
And it's okay to have static and transformational in the same story. Older, more stylized romances, certain sub-genres, and other genres across the board have multi-character stories where only one person has arc.
The thing I've noticed about transformation is when you know the end and the actual transformation, you know the beginning. If Zarek becomes open and loving at the end of Dance with the Devil, that means he needs to be closed off and suspicious at the beginning, because to create a strong arc, you have to hurt your characters where they live.
When you give someone has a life experience at the beginning of the story to threaten their view of themselves, it must be integral to how they are built. Something, somewhere in their past must reject change, and the change must address that underlying issue. Zarek wouldn't work if Astrid didn't touch the part of him that thought he was worthless. Which means that all that back story Kenyon gave him had to be there. She needed to know who he was, to know how he'd react.
Astrid was story-specific. In other words, she was built, with her own back story--to be the only one who could change this one man. Nobody else would work. Only her. Something about her, spoke to something in him.
And that's why they belong together.