No, it's not appropriate. Fanfiction should focus on positive aspects like character development, friendship, or adventure. Sexual content in fanfic about these characters is disrespectful to the source material and its fans. It can also create a negative and unwholesome environment in the fan community.
The theme of trust is omnipresent. Their trust in each other's abilities is crucial. In many fanfictions, Levi trusts Erwin's strategic plans completely, even when they seem risky. Also, the idea of redemption can be a theme. For instance, if one of them has made a mistake, the other is there to help them redeem themselves, which is a very heart - warming aspect of their relationship in fanfiction.
The fanfiction of Levi and Erwin's back story is filled with interesting details. Levi's past in the Underground gave him a unique perspective on life and survival. When he joined the Survey Corps, he brought that tenacity with him. Erwin, who was more of an idealist, was intrigued by Levi. Their back story could involve how they trained together. Erwin might have tried to instill his strategic thinking into Levi, while Levi taught Erwin some practical combat skills he learned from his tough life in the Underground. This exchange of knowledge and experiences is a key part of their relationship's development in fanfiction.
Well, usually they might focus on the romantic or sexual relationship between Erwin and Levi. But since 'lemon' implies sexual content, it's not something that should be widely promoted. However, in non - lemon fics, characteristics could include exploring their different personalities, how they interact in the military setting, and their loyalty to each other.
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.
A third theme is sacrifice. Sometimes, Erwin has to sacrifice his own needs or wants in order to help Levi. This could be in terms of time, energy or even putting himself in danger. It shows the selfless nature of their relationship in these fanfictions.