Levi's overprotection can also shape the relationships in the plot. Other characters might view Levi's actions towards Eren in different ways. Some might support Levi, thinking Eren needs that protection, while others might side with Eren and encourage him to be more independent. This can lead to various sub - plots and further development of the overall story.
To develop their relationship realistically, let them communicate. Have them have conversations about their pasts, their goals. Eren might talk about his family and his drive to avenge them, and Levi could share some of his own traumas from his past. This would create a deeper understanding between them. Also, small acts of kindness like Levi patching up Eren's wounds after a fight or Eren getting Levi his favorite tea could strengthen their bond.
The jealousy can make them more aware of their feelings for each other. When Levi gets jealous, he might start to realize how much Petra means to him. And the same for Petra. It forces them to confront their emotions instead of ignoring them.
Levi sees Eren as a complex and unpredictable character. He recognizes Eren's potential but is also wary of his intense and sometimes uncontrollable nature.
Well, in a Levi and Mikasa married fanfiction, it could be that they have a very adventurous married life. Since both are skilled fighters, they might go on missions together to protect their community. Their relationship would be based on deep respect. Levi would admire Mikasa's strength and Mikasa would look up to Levi's leadership. And when they're not out fighting, they could be teaching the younger generation their combat skills.
The fanfiction might focus on the baby inheriting certain traits from both Levi and Eren. For example, the baby could have Levi's sharp observational skills and Eren's determination. The story could also show how their friends and comrades react to the new addition to their group. Some might be overjoyed, while others might be worried about the implications of having a baby in their dangerous world.
It's hard to say. 'Levi x Eren' fanfics are quite common in certain fandoms, but the 'Levi is a criminal' aspect makes it a more specific and perhaps niche sub - genre. If there are a lot of fans who like to see dark or morally ambiguous takes on the characters, it could potentially be popular within that subset of the fandom. However, it also might not be mainstream popular as it goes against the more typical heroic portrayals of the characters.