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.
I'm not sure who exactly Charles Falco is without more context. There could be many people named Charles Falco. Maybe he's a local figure in a specific community, an artist, or someone involved in a particular event.
Love and friendship is a big theme as well. Their relationship can be seen as a deep friendship that has the potential to turn into love. Fanfics explore different aspects of this, from the awkward first moments of realizing there are deeper feelings, to the more mature and stable relationship they could have in the future.
One common theme is friendship. They are both characters from the Smash Bros. series, and many fanfics explore their relationship as comrades, like going on adventures together in the Smash universe.
One great Star Fox Falco and Katt fanfiction is 'Falco's New Adventure with Katt'. It's really engaging as it shows their relationship developing during a dangerous mission. The story has a lot of action and also some really sweet moments between them.
I'm not sure about specific popular 'Falco gay fanfic' stories as it depends on different fan communities. You could try searching on dedicated fanfic platforms or forums related to the character Falco to find such stories.
I think it's a rather odd and unique concept. Maybe this Falco has some sort of special power related to gas or is known for causing comical chaos with its gaseous abilities.
It depends on your skills and strategies. If you have a good understanding of the game mechanics and can execute your plans effectively, it might be possible.
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.