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.
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.
Perhaps it's a group of bandits who don't really understand who Mikasa is. They just see her as a valuable hostage to get what they want from the military or the local communities. They might be after food, weapons, or just a large sum of money in exchange for her safe return.
It could be Orochimaru. He has always been interested in Naruto's power and potential. He might kidnap Naruto to try and extract the Nine - Tails' chakra or study his unique Uzumaki bloodline further. Another possibility is a group of rogue ninjas who want to sell Naruto to the highest bidder, thinking his value as a Jinchuriki would make them rich.
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.
The kidnapper could be an estranged family member of Beckett. There might be some family feud or inheritance issue that leads them to believe that by kidnapping the baby, they can gain an upper hand. Or it could be a completely random person who has a mental disorder and randomly targeted Beckett and the baby because they saw them as an easy target.
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.
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.
The Grimm could also be involved in an unusual way. Perhaps a new type of Grimm that has the intelligence to kidnap. They might be working with a human or Faunus villain who has some sort of control over them, and they take the character to an unknown location where the RWBY team has to face not only the Grimm but also the mastermind behind it.
It could be a vengeful god or goddess. Maybe one who has a grudge against the demigods in general and sees Annabeth as an easy target to send a message. For example, a minor god who feels overlooked and wants to prove their power by kidnapping such a well - known demigod.