A common element is also the change in the characters' worldviews. As they experience the outside world, their beliefs about themselves, their enemies, and their purpose in life can be completely transformed. For instance, a character who was once solely focused on killing Titans might start to question the morality of it all when they learn more about the outside world and the Titans' place in it. Also, there could be new power dynamics at play, like the Scouts having to negotiate with powerful outside groups instead of just fighting Titans.
Many fanfics about the outside world in Attack on Titan focus on the characters' reactions to this new and strange environment. They might struggle to adapt, or they could find that their skills and knowledge from inside the walls are either very useful or completely useless. Some fanfics may also explore the relationships between different groups in the outside world, like how the Scouts interact with other human settlements that have different values and ways of life.
One common theme is survival. Just like in Attack on Titan, the characters in these fanfics often have to fight for their lives against the Titans. For example, in many fanfics, the Hetalia characters use their unique skills to try and survive in this dangerous world.
One common theme is the clash of different power systems. For example, when crossing over with a magic - based series, the contrast between the Titans' brute force and magic is explored.
One common theme is power struggle. Both 'Attack on Titan' and Marvel have characters with great powers. In the fanfics, it's often about how the powers from 'Attack on Titan' like the Titan - shifting abilities compare and interact with the superpowers in Marvel.
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.
One common theme is identity. The trans characters often struggle with their identity in a world full of danger like Attack on Titan. They have to come to terms with who they are while also fighting Titans.
Well, it's a really strange concept as Attack on Titan is a fictional entity and can't actually 'watch' a fanfic. But if we were to be creative, maybe it would be like the characters in the series are observing an alternate version of their own story. They might be shocked, amused or even inspired by the different plotlines and characterizations in the fanfic.
One possible fanfic could be about Mikasa's transformation into a Titan being a unique situation in the 'Attack on Titan' world. Maybe she has different abilities compared to other Titans. For example, she could retain more of her human consciousness and use her combat skills in Titan form. This would create an interesting dynamic as she tries to protect her friends while being a Titan, which is usually seen as an enemy.
Power struggles are also a common theme. In 'Game of Thrones', it's about the Iron Throne, and in 'Attack on Titan', it's about controlling the Titans or the truth behind them. Fanfic might explore how the power - hungry characters from 'Game of Thrones' would react to the power dynamics in the 'Attack on Titan' world, like Cersei trying to manipulate the Titan - shifters.
One common theme is loss. Given the brutal world of Attack on Titan, Levi might cry over the loss of his comrades. His close relationships with his squad members make their deaths a heavy blow.