Lizzy might be a person who has had a significant impact on the author's life. She could be a neighbor who was always there to help, and over time, the narrator developed deeper feelings for her. It's also possible that she's someone the author met during a trip, and they had a special connection from the start.
Ciel would likely become more protective. He has always been in a dangerous world, and now with a baby on the way, he'll do whatever it takes to safeguard his family. Lizzy, she might become more nurturing. She was already a strong character, but motherhood could bring out a softer, more patient side of her.
The plot of the Lizzy and Diesel novel is full of mystery and adventure. It follows Lizzy and Diesel as they solve complex puzzles and face unexpected challenges.
The plot also matters. A fanfic could be about their relationship evolving during a dangerous mystery they have to solve together. This gives the story an exciting backdrop and allows for interesting interactions between the two characters. It should have a good balance between their personal relationship growth and the external events happening around them.
Another reason could be that fanfiction gives them a sense of community. By loving and reading fanfiction, they can connect with other fans who have similar interests. They can discuss their favorite stories, share their thoughts on different interpretations of their characters, and feel part of a bigger group.
One of my favorite scenes in Ciel x Lizzy fanfiction is when Lizzy stands up for Ciel in front of others. It shows her loyalty and her growth from a somewhat sheltered girl to someone who can be a protector. Another great scene is when Ciel lets his guard down a little around Lizzy, like sharing a quiet moment in the garden. It's a rare moment of vulnerability for him.