A little ant could be one of the main characters. Maybe the ant is curious about the ladybug's pregnancy and offers to help in any way it can. Another could be a wise old beetle that gives the ladybug advice on how to take care of herself during pregnancy.
One plot idea could be that the pregnant ladybug is on a journey to find a special place to lay her eggs safely. Along the way, she meets different bugs who either help or hinder her. Another could be that she has to protect her unborn babies from a predator in the garden.
Well, a frequent theme is the anticipation of motherhood. In the fanfiction, Ladybug might be shown as being both excited and nervous about becoming a mother. She could be seen preparing for the baby, like making a little nursery in her secret hideout. There's also the theme of the baby's powers. Some fanfictions might explore if the baby inherits her powers or has some new and unique abilities. And then there's the theme of how the city she protects reacts. Do the people start to notice that Ladybug is different? Do they try to help or protect her in some way because they know she's pregnant and vulnerable?
One common theme could be the challenges and joys of pregnancy. It might explore how Ladybug deals with the physical and emotional changes. Another theme could be the support she gets from her friends and allies in the MLB universe.
Another possibility could be a new character introduced specifically for the fanfiction. Maybe a powerful and charming hero from another city comes to Paris to help Ladybug and Chat Noir. He and Ladybug develop a connection, and he could end up being the father. This would create a lot of drama and new storylines, especially when it comes to how Chat Noir reacts to the situation.
One possible plot could be Marinette dealing with her superhero duties while being pregnant. She might have to be more cautious in battles, and her teammates could be extra protective. For example, Chat Noir might be constantly on the lookout for any danger that could harm Marinette and the unborn baby.
The relationship with Adrien is a huge theme. It could be about how they navigate their relationship when this big change occurs. Some fanfictions show them having to grow up quickly and become more responsible for each other and the baby. It also might explore how their identities as Ladybug and Chat Noir play into their new family situation.
Chat Noir is an obvious choice. His relationship with Ladybug is so central to the original story, and with her pregnant, his reactions and support would be a great addition. Marinette's best friend Alya could also be included. She could be the one Ladybug confides in, and Alya could use her journalistic skills to help keep Ladybug's pregnancy a secret if needed. And Master Fu could be in the story. He could offer his wisdom and guidance, especially when it comes to any potential threats to Ladybug or the unborn child.
If the fanfiction takes a really wild turn, it could be that the father is a sentient Miraculous. I know it sounds strange, but in the world of fanfiction, anything is possible. Maybe the Miraculous has some sort of power that allowed it to impregnate Alya in a very unique and magical way, and the story then delves into how Alya and her friends deal with this extremely unusual situation.
Well, it could be about Alya dealing with the challenges of being pregnant while still being involved in the superhero chaos. Maybe she has to keep it a secret from the villains who might use it against her. Or perhaps she discovers some new powers related to her pregnancy that help Ladybug and Chat Noir in their battles.