I don't know for sure as I haven't read the book, but likely the girl herself is a main character.
The most obvious main character is the girl the title refers to. However, there could be other significant characters. For instance, a mentor figure who guided her during a difficult time in her past. Or perhaps a rival who made her strive to be better. Without reading the novel, it's hard to be certain about all the main characters, but it's reasonable to assume that the people who were closest to the girl in her past and had an impact on her journey are among the main characters.
Since the title is 'the girl i used to be novel', the girl in question is surely a main character. There may also be other characters like her family members, such as her parents or siblings who could have played important roles in her life. Maybe there are friends or love interests that influenced her development and are thus important characters in the story.
Often, there will be a sidekick or a friend - type character who helps the former final boss in their new journey. This character can provide support, ask questions that the readers might have, and be a source of comic relief or emotional connection. And don't forget about any potential new antagonists who may rise up against the now - changed final boss.
I don't know for sure. Maybe there's the girl the title refers to, and perhaps a love interest or a friend.
Since the title is 'I decided to become a perfect girl novel', the central character is most likely the girl with this aspiration. There could be other characters like a mentor figure who guides her on this journey, or perhaps a rival who makes her strive harder to reach that perfect state. Maybe there are also friends who are with her through the ups and downs of her transformation process.
I don't know the exact characters in 'the snow girl novel' since I haven't read it. But there must be the snow girl herself as the main character. There could also be other characters like a love interest, perhaps a young man who is intrigued by her uniqueness.
I don't know as I haven't read it. But it could be the summer girl herself, her friends, and maybe her family members.
There is also her mentor, who plays an important role in guiding her and helping her understand her powers better. He has a wealth of knowledge and experience that he imparts to her.
Since I don't know the exact 'golden girl novel', I can't say for sure. But it would likely have the 'golden girl' as one of the main characters. There might also be a love interest, like a young man who is drawn to her unique qualities.
The central character is the girl on the train. She is a complex character with her own issues. Then there are the two people in the house she watches from the train, a man and a woman. Their actions and relationship are key elements in the plot as the girl on the train tries to piece together their story.
Since we have no details about the 'fly girl novel', the main characters could be a group of friends that the fly girl has. They could be involved in all kinds of escapades together. Or it could be that there's an antagonist, someone who tries to stop the fly girl from achieving her goals, and this antagonist would also be a main character in terms of driving the plot forward.
The main character is Rachel, a woman with a drinking problem and a troubled past. There is also Megan, the woman Rachel spies on from the train. And Scott, Megan's husband.