It's fairly common. Fans often look for more content related to their favorite shows. Since 'Attack on Titan' has a large and passionate fan base, there are a lot of fanfics available. 'Aot' fans might watch (read) these fanfics to explore different scenarios that the official story didn't cover. For example, they might want to see how a certain character would react in a different situation or what would happen if a major plot event had a different outcome.
There could be various fanfictions. Maybe some that focus on alternative endings, like ones where certain characters survive who didn't in the original. For example, a fanfiction where Erwin survives and leads the Scouts in a different way.
One great Niccolo x Sasha fanfic could be 'A Culinary Bond'. In this fic, Niccolo's cooking skills are used to bring him closer to Sasha. Their relationship develops as he creates special dishes just for her. Another might be 'Under the Stars', where they have a chance encounter while stargazing and start to realize their feelings for each other.
You can start by looking on fanfiction.net. It has a large collection of fanfics from various fandoms, and there's a good chance you'll find some Niccolo x Sasha ones there. Another option is Archive of Our Own (AO3). It's known for its wide range of fan - created content and has a great tagging system to help you find exactly what you're looking for.
It could mean that a person who is a fan of 'Attack on Titan' (AOT) is reading or watching fan - created fictional works related to AOT. Maybe they are interested in seeing different interpretations or storylines that fans have come up with.
One way is to check on popular fanfiction websites. Look for ones with high ratings and a lot of reviews. For example, Archive of Our Own (AO3) has a large collection of AOT fanfictions. You can search for the most popular ones there.
Definitely not. AOT is a work of fiction that combines elements of fantasy, action, and drama. It's set in a made-up world with its own unique plot and characters.