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.
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.
The plot of the first episode was about the modern business elite Yin Ning who accidentally transmigrated to the Wu Dynasty and became the son-in-law of the merchant family, Ning Yi. His wife, Su Tan 'er, was busy with the cloth business and did not even have time to attend their wedding night. However, there were many undercurrents hidden in this novel world. Ning Yi followed the Su family and was involved in the fierce battle between the royal merchants, the disputes of the martial world, and the game of the court. In the first episode of the live-in son-in-law, the story of Ning Yi and Su Tan 'er began to unfold.
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.
The AOT manga has finished. It wrapped up all the major plotlines and provided a conclusion to the story that fans have been following for a long time.