Perhaps it's a way for the author to explore different themes and challenge conventional character archetypes. The decision for her to be a villainess might be to create tension and drama in the manga's narrative.
The main character is, of course, the villainess herself. She is at the center of the story. There might also be a love interest, perhaps a nobleman or a prince. And then there could be other antagonists who oppose the villainess in her new - found journey, like jealous rivals or those who want to uphold the status quo.
The world - building in 'I will live the life of a villainess novel' is a significant feature. It might create a fictional world with its own set of rules, hierarchies, and social norms that the villainess has to navigate. Also, the relationships in the novel are interesting. There could be complex love - hate relationships, rivalries with other characters, which all add to the overall intrigue of the story.
The plot mainly revolves around the protagonist who finds herself in the role of a villainess in a story. Instead of following the original doomed path of the villainess, she decides to change things and just live her life as best as she can in this new situation.
First, you need to come up with a unique and interesting character design for the villainess. Make her have complex motivations and personality traits. Also, think of a captivating plot that keeps readers engaged.