Perhaps a female soldier who catches Stiles' eye. She could be a skilled combatant and have a complex personality. Their relationship, whether it's a friendship or something more, could be a major part of the story as they both navigate their military careers.
Another main character could be Stiles' best friend from his pre - army days who also decides to join the army with him. They would support each other through the tough training and face the challenges of military life together.
There could be a tough drill sergeant who acts as a mentor and a source of conflict for Stiles. This character would be strict but fair, and would push Stiles to his limits.
Well, one possibility is that Stiles could be facing some inner turmoil at home or in his personal life, and joining the army becomes his way to find purpose and discipline. He might start as a clumsy recruit but gradually grow into a strong and reliable soldier, making new friends and facing various challenges along the way.
In many 'Stiles is not human fanfiction', Malia could play a significant role. Given her own complex backstory and her were - coyote nature, she might be able to relate to Stiles in some ways if he's not human. She could either help him adapt to his new state or be in conflict with him. Kira could also be involved. Her kitsune powers and her kind nature might lead her to try and understand Stiles. And the Sheriff, Stiles' father, is bound to be in the story. His relationship with Stiles would be put to the test as he discovers his son is not what he thought he was, and he'd have to deal with his own emotions and the potential danger that Stiles' non - human nature could bring.
There could be other members of Peter's pack such as Derek. Derek often plays an important role in stories related to packs. He might be initially skeptical of Stiles being part of the pack.
Well, aside from Stiles, Scott is bound to be a central character. Their friendship is so strong that Scott would immediately start looking for ways to rescue Stiles. Derek Hale is another likely character. Given his past with the alpha pack and his relationship with Scott and Stiles, he would have a role to play. Then there's Allison. Her family's history with the supernatural means she has skills and knowledge that could be useful in rescuing Stiles. She could be involved in the search and rescue operation, using her archery skills and knowledge of the supernatural world to help out.
Luna Lovegood would be a great pairing. She's quirky and open - minded, and her unique perspective could complement Stiles' inquisitive nature.
Another possible main character could be the base commander. Let's say Commander Smith, who notices Bella's potential and gives her special tasks or opportunities, which then drives the story forward as Bella has to prove herself worthy of these tasks.
Stiles is a must - have main character. Then, depending on the direction of the fanfiction, characters like Simon Lewis could be important. Since Simon is a vampire in the Shadowhunter universe, his interactions with Stiles, who is new to this world, could be really interesting. Also, characters like Luke Garroway, the werewolf, might play a role, especially if the story involves the relationships between different Downworlder groups and Stiles' place in all of that.
Perhaps he feels that the other pack can offer him more opportunities for growth. In some fanfictions, the new pack might have access to different kinds of magic or knowledge that Stiles is eager to learn. So, he joins them to expand his skills and understanding.
Stiles' father could be a major character. He would be worried sick about his son and use all his resources to try and find him. Maybe he teams up with some of Stiles' friends like Scott or Lydia.
One possible plot could be that Stiles and Derek's relationship has developed over time. Stiles discovers he has a son, perhaps from a past encounter he didn't expect to have consequences. Derek, being a werewolf with a strong sense of family, steps in to help Stiles raise the child. They might face challenges from the supernatural world, like other werewolves or creatures who see the child as a threat or an opportunity. And along the way, their relationship deepens as they bond over the care of the son.