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.
I'm not sure which specific 'Pieck Finger fanfic' is the best. You can try looking on some popular fanfiction websites like Archive of Our Own. There might be a variety of stories there.
Often, there might be themes related to her abilities and how she uses them in different situations. For example, in battle or when facing challenges. Another theme could be her backstory and how it shapes her personality and actions in the fan - created stories.
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.
A common theme is loyalty. Given their comradeship in the series, fanfictions often explore how their loyalty to each other extends beyond just being fellow soldiers. Another theme could be sacrifice, as they are in a dangerous world where they might have to sacrifice for one another.
One common theme is loyalty. Pieck is often depicted as being loyal to her comrades and her cause. Another theme is sacrifice, as she is in a situation where she may have to give up a lot for the greater good.