Well, perhaps in the fanfic, Armin is kidnapped by a secret organization within the walls. This organization believes Armin has some special knowledge about the Titans that they can use to their advantage. They keep him in a hidden location and try to interrogate him. Armin, being smart, might try to outwit them while his friends from the Survey Corps are desperately searching for him.
One possible plot could be that Armin is kidnapped by a group who oppose the Scouts. They might want to use him as a bargaining chip against the Survey Corps. Maybe they hope to exchange him for some valuable information or resources that the Scouts possess.
In the fanfic, it could be that Armin is kidnapped by a rogue group of soldiers who have their own agenda. They think that Armin's strategic mind could help them achieve their goals, which might be related to overthrowing the current military leadership or finding a new way to deal with the Titans. His friends, Eren and Mikasa, would then embark on a dangerous mission to rescue him. They would face many challenges and obstacles along the way, such as the kidnappers' well - guarded hideouts and possible traps.
Another possibility is that the kidnappers are a group of foreign spies. They come from a land outside the walls that has its own interests in the situation inside. They believe that Armin holds valuable information about the Titans and the technology within the walls. So they kidnap him to take that knowledge back to their own people.
A great plot for such a fanfic could be that Mikasa's Titan form is a result of a connection to an ancient Titan power. As she becomes a Titan, she starts to have visions of the past, of how the Titans came to be. She then decides to use this knowledge and her new form to try and end the Titan - human conflict once and for all. Along the way, she has to face her friends who are initially scared of her but eventually come to accept her new form as she proves that she is still the same Mikasa deep down, just in a different body.
Another scenario could be that Mikasa is kidnapped by a group who wants to use her as a bargaining chip against the military. They might demand a large amount of resources or the release of certain prisoners. Meanwhile, Mikasa, being the strong - willed character she is, would be constantly looking for a way to escape. She'd use her combat skills and intelligence to try and outwit her captors at every turn.
In 'Attack on Titan' fanfics about Eren and Armin, their relationship is often complex. Eren is usually depicted as a strong - willed and sometimes impulsive character, while Armin is more of the intellectual type. Their bond can be seen as a contrast of power and intelligence. In many fanfics, they support each other through difficult times, with Armin providing strategic advice and Eren being the one to execute plans. Their friendship is a key aspect that drives the story forward in these fan - created works.
One possible plot could be that the ponies accidentally end up in the Attack on Titan world through some sort of magical portal. They then have to figure out how to survive in this harsh environment. They could use their unique pony abilities, like Fluttershy's connection with animals, to try and understand the Titans better. Maybe they could even find a way to communicate with the Titans and find out if there's a way to stop the attacks without all the bloodshed.
One common theme is loyalty. Armin and Erwin are both extremely loyal to their comrades and to each other. In fanfics, this loyalty often becomes a central aspect of their relationship. Another theme is leadership. They are both leaders in their own ways, and fanfics might explore how they lead together or support each other's leadership.
One common theme is redemption. Annie has done some pretty bad things in the series, and in many fanfics, Armin is a key figure in her journey towards redemption. Another theme is love in the face of chaos. Given the world they live in, filled with Titans and danger, their love is often portrayed as something that can survive and even thrive in such a harsh environment. Also, the theme of understanding each other's pasts is quite common. They both have complex backstories, and fanfics often explore how they come to understand and accept each other's past traumas.
One common theme is the exploration of the blurry line between friend and foe. Since the Female Titan is initially an enemy, fanfictions often delve into whether she can become an ally through her interactions with Armin. For example, Armin might try to convince her to side with the humans.
In the Attack on Titan manga, Armin is still alive. His character plays an important role and continues to be part of the story's progression. There are many close calls, but he manages to come out unscathed.
Some fanfics might explore a romantic relationship between them in a more secretive or forbidden way. Given the military setting and the overarching plot of Attack on Titan, their relationship might be something they have to hide. This adds an element of tension and drama to the story, as they navigate their feelings while also dealing with the threats of the Titans and the politics within the walls.