One of the best moments could be when they have a picnic in the park as described in some fanfictions. They share their favorite foods and just enjoy each other's company under the warm sun.
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.
One key moment was when they first realized their feelings for each other during a particularly tough battle. Another was when Cyclops defended Jean against the doubts of other X - Men members. Also, the times when Jean used her powers to save Cyclops in dangerous situations were important in their love story.
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 key moment was his role in 'Bloodsport'. It really put him on the map as an action star. His martial arts skills were on full display, and it attracted a large fan base. Another important moment was when he started to diversify his roles and work with different directors. This showed his growth as an actor.
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.