One possible plot could be that the girl has amnesia and the scar is the only clue she has about her past. As she tries to figure out how she got the scar, she discovers a world of secrets and lies. People around her act strangely when she asks about it, which makes her more determined to find out.
I haven't read this specific fanfic, but generally, a 'girl with a scar' in a story often symbolizes some sort of past trauma or mystery. In a fanfic context, it could be related to the original source material's themes, like a character who has been through a difficult event and is now dealing with secrets and lies as a result. Maybe the scar is a physical reminder of something she wants to hide or something that others are using against her.
It could be that in the story, the girl's friends were keeping secrets from her. For example, they might have been spreading lies about her behind her back, like saying she was a bad influence when she wasn't. The secret part could be that they were jealous of her for some reason, like her good looks or intelligence.
One possible plot could be that as a girl, Deidara faces different challenges in the male - dominated ninja world. Maybe she has to prove herself more than her male counterparts. Another could be that she forms different relationships with other characters. For example, her interactions with Sasuke might change due to her being a girl.
One possible theme could be betrayal. With secrets and lies, there's a high chance of someone being betrayed by another character. Another theme might be self - identity. As the girls deal with their secrets, they may also be struggling to find out who they really are. And of course, the theme of friendship could be there too. How do secrets and lies affect their friendships?
She might initially be in denial. For example, if she hears lies about herself, she may not want to believe that her friends could be so cruel. So she pretends that everything is okay.
The themes likely include pain and suffering. Since the girl is broken, the secrets and lies have probably caused her a great deal of emotional pain. Additionally, the theme of truth - seeking is probable. As the story unfolds, she may be on a quest to find the truth behind all the secrets and lies. And there could be a theme of isolation, as she might feel alone in dealing with all these issues.
Perhaps one theme is the shattering of innocence. If it's about a girl, she may have started out innocent, but the secrets and lies around her have broken that innocence, making her grow up faster and face the harsh realities of the world.
Maybe in a magical world fanfic, the girl is a fairy and she encounters a strange little creature. The creature, thinking she is a friend, licks her face as a sign of greeting. This event then sets off a series of adventures as the girl tries to figure out what the creature is and what it wants.
One possible plot could be that the 'gagaga girl' discovers she's pregnant unexpectedly. She then has to deal with the reactions of her friends and family. Some might be supportive while others are judgmental. She has to make decisions about whether to keep the baby or not, all while trying to figure out who the father is.
In a fanfic, it could be that the girl is from a magical world where dinosaurs are brought back to life through magic. A small, cute dinosaur licks her as a sign of friendship. The girl then discovers that she has a special connection with the dinosaurs and has to use this connection to stop an evil wizard who wants to use the dinosaurs for his own dark purposes.