Who could Stiles meet first when he returns to Beacon Hills in fanfiction?

Well, one possibility is that he comes back to help his old friends deal with a new supernatural threat. Maybe there's a powerful and mysterious creature that the remaining pack members can't handle on their own, and Stiles' return is the key to their survival.

There's also a chance that he'd meet Lydia first. Lydia has her banshee powers, and she might be drawn to Percy because of his otherworldly presence. She could sense something about him that's not of this world, and approach him out of curiosity. Their meeting could be a very intense and mysterious one, with Lydia trying to figure out what exactly Percy is.

One possible reason could be to protect his friends. Maybe he discovers a new threat that is specifically targeting him, and he decides to leave Beacon Hills to draw the danger away from those he loves. For example, in some fanfictions, a powerful and vengeful supernatural being might be after Stiles, and he believes that by leaving, he can keep his friends safe.

He could meet Scott McCall. Scott, being a werewolf, would be intrigued by Harry's magic. They could become friends and learn from each other. Harry could help Scott better control his werewolf side using magic, and Scott could show Harry how to survive in Beacon Hills' supernatural chaos.

He could meet Hinata, and their relationship might develop further. Maybe she would be the first to greet him and express her admiration more openly.

He might meet Iruka first. Iruka was always like a father figure to Naruto, and it would be a very heartwarming reunion. Iruka would probably be one of the first people to welcome Naruto back with open arms.

The Nogitsune could also be a great antagonist. It thrives on chaos and mischief. Percy's presence and his powers would be something the Nogitsune would want to either corrupt or use for its own evil purposes. It could try to possess Percy or those around him to gain access to his demigod abilities.

The town of Beacon Hills itself might be affected. Stiles was always in the middle of things, helping to solve supernatural mysteries. Without him, there could be an increase in unexplained events. And some of the townspeople who knew Stiles, like Sheriff Stilinski, would be deeply affected on a personal level, with the sheriff possibly becoming more overprotective of the remaining youth in town.

They're compelling because they offer new perspectives on the characters and the town. It's interesting to see how things change without Stiles.

He might meet his old owl, Hedwig, if she's still alive in the fanfiction. It would be a very heartwarming reunion.