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.
Maybe Levi is a criminal in the sense that he's part of an underground rebellion against an unjust regime. Eren, who is initially on the side of the establishment, meets Levi and gradually comes to understand his motives. Their relationship could develop as Eren has to decide whether to side with Levi or stay loyal to the regime, all while a romantic connection forms between them.
Yes, there could be such fanfics in the fandom. Writers often like to explore different aspects of characters, and making Levi secretly a girl is an interesting and creative take. It might involve reimagining his backstory, relationships, and how other characters would react to this secret.
A great Levi fanfic often has a deep understanding of his character. For example, it should capture his stoicism and his fierce loyalty to his comrades. If it can show his internal struggles and how he overcomes them, that's a plus.
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.
One idea could be a story where Levi and Eren are on a dangerous mission together. They start off not getting along well due to their different personalities. Levi is strict and methodical while Eren is impulsive. But as the mission progresses, they gradually learn to understand and rely on each other. For example, Eren might save Levi from a Titan in a moment of quick thinking, and Levi in turn teaches Eren some crucial combat skills.
There's also 'Levi's Redemption'. This fanfic focuses on Levi's past traumas and how he overcomes them. The author does an amazing job of portraying his complex personality and his relationships with other characters in a very believable way. It's a must - read for any Levi fan.
One common theme is loyalty. Levi is a very loyal character in the original 'Attack on Titan' series, and fanfics often explore his loyalty to his comrades, his cause, and his friends. For example, in many fanfics, he will go to great lengths to protect his fellow Survey Corps members.
One common theme is friendship. Since Cath and Levi are often the main characters, their relationship development, be it from strangers to friends or strengthening their existing friendship, is a popular theme.
One great AOT female Levi fanfic is 'The Captain's Heart'. It delves into a unique story where a female character has an interesting relationship with Levi. The writing is engaging, and it really captures the essence of the Attack on Titan world while exploring a different side of Levi's character.