Writing a supporting character - looking for advice on how to improve her characterization.

I've been writing a story, set in an Alternate History 1997, with the setting being the U.S. (undecided between Texas, California, Arizona or New York City) and it follows a group of five female protagonists (The Protagonist is a journalist who covers the stories that aren't flashy, but still cover hot-button issues).

I'm looking for advice on how to improve this character.

Here's what Rachel's character biography would look like if it was on a work's page:

Rachel is a 23-year-old woman from Dallas that Jenny, The Protagonist meets while in Los Angeles.

She appears early on in the story.

• Adorkable: Has a tendency to geek out over food and drink, and behaves in such a way it's adorable.
• Alternate Identity Amnesia: She doesn't remember what she did as Allison, and vice versa.
• Ambiguous Disorder: She mayhave Asperger's Syndrome, but it's not entirely clear In-Universe and the issue isn't discussed either.
• Asian and Nerdy: Well, 1/4 Japanese.
• Berserk Button: Being accused of being "prissy" or making fun of her Canadian accent or being Canadian. Downplayed in that she uses Tranquil Fury.
• Canada Eh: She's from Toronto and has the accent to go with it. However, she's a dual U.S./Canadian citizen anyway.
• Girly Girl: Zig-zagged, but her shared interest with Jenny in cars puts her as possibly Girly Girl with a Tomboy Streak.
• If It's You, It's Okay: Dates Shelby-Marie, aged 26, despite not normally being attracted to women. Although, this may be more of a case of her not being open about her attraction to women. Justified as it is the 1990s. Her dating Shelby-Marie becomes a plot point in itself.
• Lolita Fashion: Of the Classic Lolita and Casual Lolita type - which she wavers between.
• Mixed Ethnicity: She's American-Canadian and partially Japanese too.
• Omniglot: English, Canadian French and Spanish.
• The Smart Girl: Intelligent, whichever side of Split Personality.
• Southern Belle: A Canadianized variant of this type, albeit the modern type.
• Split Personality: Curiously, not a case of Jekyll & Hyde or Superpowered Evil Side type of this trope as her two split personalities are both Nice Girl types.
  • She has the alternate identity "Allison Weiss" (surname may be changed) who's something of an over-the-top, Perky Goth despite not being Raven Hair, Ivory Skin.
  • Her second split personality, Rebekka "Bekki" De (surname undecided), is a Functional Addict Big Eater who thrives on sugary foods, WISE potato chips and alcohol. She's also a somewhat Hard-Drinking Party Girl.
• Statuesque Stunner: She's 6"3 (1.92m) in height.
• Those Two Girls: Her and Jenny, the protagonist.
• Trademark Favorite Food: Snack foods, and surprisingly she doesn't get too overweight from them.

She's going to become important as the story progresses, but how can I expand her characterization in a way that makes it interesting and realistic?

First thing that popped into my mind when I saw this thread was a question. "What's her backstory?" In what context did she exist? Where is she coming from? What her family is like? What her childhood was like? What her relationship with her peers was like in adolescence?

People don't exist in a vacuum. Our character traits are a combination of genetics and learned behavior. When you'll figure out what kind of journey your character has made before the start of the story, you'll find your answer. You then will be able to figure out how her traits will tie into the journey that is before her. The latter part is especially important, since if a thing in your story (up to and including characterization) doesn't affect the plot in any way, then it doesn't need to be there.

Second and third questions are "what does she want?" and "how she usually gets things she wants?" They deal with the destination your character has set for herself and the way she gets to that destination. Does she want to be rich, for example? If she does, what is she willing to do to achieve that? Just through hard honest work or she is willing to throw other people under the bus to get what she wants? Answering those question will help you in getting insight into the psyche of your character, help you flesh them out more.

Hope this helps.

@ Millership:

Her backstory is she's a 23-year-old in college, wants to be a researcher (of the TV/media, not medical, kind) and she's a Nice Girl with four sisters back in Markham/Toronto, Ontario Canada that she doesn't see as often.

As for her goal, well, it varies, depending on which side of the Split Personality:

• Rachel: Wants to work as a researcher in the media, prepared to work hard, doesn't mind researching the unglamorous stuff.

• Allison: Wants to be a glamor model. But she also wants a stable relationship.

• Rebekka: Wants to get into high society and date a beautiful high-society woman. She speaks with a thick Vancouver accent, which is different to Rachel's accent.

Her other two Split Personality selves are both Nice Girl types, like Rachel. However, they're louder and brasher than Rachel.

This is the starting point; it's how to work the Split Personality into the story without cliches that's the hard part, since there's no guide on here about writing a split personality character.

Okay, then ask yourself how she came to be possessing this Split Personality. This is a serious (and poorly researched) personality disorder, which generally does not just pop into existence all of a sudden. I advise you to do some research on Dissociative identity disorder, in order to get the answers.

Oh, absolutely. For this, research, and a ton of it, is necessary. Also, don't think of this character as "the character with MPD". Think of them as "A character who just so happens to have MPD". Don't put the disorder first. They're still a character first and foremost, not just a walking medical diagnosis.

The disorder is secondary anyway.

The explanation for her Split Personality comes from bullying in high school, personalities created to cope with the bullying, plus she went to a different school than her sisters who are older than her (does the school thing count as Artistic License – Law? No idea on Canadian schooling here!)