A major theme is often power. Since he's not human, he might have special powers. The fanfictions explore how he uses or struggles with these powers. Also, the theme of secrecy comes up a lot. Stiles may need to keep his non - human side a secret from some people, which creates a lot of tension.
Scott is often paired with Stiles. Their friendship is a central part of the original series, and in fanfiction, it can be explored in new ways when Stiles isn't human. Scott might have to deal with the changes in Stiles and still maintain their bond.
Another plot could involve Stiles trying to hide his non - human nature from his friends, especially Scott. This would create a lot of tension and secrecy in the story. He'd have to constantly come up with excuses for his strange behavior or powers.
One great 'Stiles isn't human' fanfiction is 'Stiles, the Hidden Creature'. It delves into Stiles being a powerful and mysterious non - human entity. Another is 'Stiles' True Nature' which shows his journey of discovery about his non - human side.
One interesting idea could be exploring how Lucy, not being human, views the human world. Maybe she has unique perspectives on human emotions like love and friendship that are different from our own.
One possible plotline could be Hermione being a magical creature in disguise. Maybe she's a veela, which would add an interesting dynamic to her relationships. Her beauty would be even more alluring and it could cause some jealousy among her peers.
He could be a demon. In some fanfictions, Naruto might be reimagined as a powerful demon with unique abilities that are different from his normal human ninja skills.
One interesting 'eren isn't human fanfiction' could be where Eren is some kind of ancient spirit reborn. In this story, he has powers that are beyond human comprehension and he uses them to protect his friends in a very different way than in the original plot. His non - human nature makes his actions more unpredictable and the story full of twists.
If Naruto is a non - human, say a god - like being. The plot could develop around other characters' reactions to his true nature. Some might fear him, while others might try to use his power for their own gain.
Draco Malfoy could be another character. His interactions with Hermione would be full of tension. If Hermione is non - human, he might be even more jealous or spiteful, or perhaps he could develop a begrudging respect for her unique abilities that set her apart from ordinary witches.