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.
" Sister Li's Bastard Superpower World " was a web novel. The story was set in a different environment from the real world. Everyone had a superpower, but these superpowers might not be practical. There were all kinds of strange superpowers in the story, such as special effects caused by specific actions at specific times and places, or 39 consecutive backflips that would cause death and soul separation. The plot of this novel was very imaginative, funny, and interesting. The author had added many unexpected elements to it. However, other than this information, the given search results did not provide more specific content and explanations about Sister Li's Bastard Superpower World.
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.