Well, if Levi turns into a girl in the fanfiction, his fashion sense could be an interesting aspect. Maybe he would start wearing different types of gear. Instead of his usual plain style, he could end up with something more stylish yet practical. Also, his interactions with female characters would take on a whole new dimension. He might be able to better understand the struggles that female soldiers face in the Survey Corps. This could lead to him advocating for more equality within the military ranks.
His role in the Survey Corps might change in terms of the tasks he's assigned. He could be used more for intelligence - gathering missions that require a different kind of approach. Since he's now a girl, he might be able to infiltrate certain areas more easily where male soldiers would draw too much attention.
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.
In a Levi love story within Attack on Titan, Levi is often seen as a complex and stoic character. His love, if there was one, would be filled with his typical no - nonsense attitude. He might show his love through protecting someone in his own gruff way, like how he protects his comrades in the Survey Corps.
One possible plot twist could be how his relationships change. For example, his friends might react with shock and confusion at first. Mikasa might have a whole new set of emotions to deal with, like a different kind of protectiveness. Also, the military might view him differently. They could be hesitant to send a 'female - Eren' into battle at first, or they might use his new form to their advantage in different ways, like using his appearance to deceive the Titans.
In Attack on Titan fanfiction, Levi and Mikasa's relationship can be quite interesting. They are both strong and skilled fighters. Their relationship might start from mutual respect for each other's abilities. Levi could see Mikasa's determination and be reminded of his own. Mikasa, on the other hand, might look up to Levi as a more experienced and powerful comrade. In some fanfictions, their relationship could develop into a deep friendship or even a romantic one, with them relying on each other in the face of the Titans and the complex politics within the walls.