A good one often has well - developed characters. For example, Sabrina's protective nature should be shown in a believable way, like how she defends Ash from other powerful Pokemon trainers or dangerous situations. Also, the relationship between Ash and Sabrina should grow organically. It shouldn't feel forced.
You can try looking on fanfiction websites like FanFiction.net or Archive of Our Own. They usually have a large collection of Pokemon fanfictions, and you might be able to find the Ash x Protective Sabrina ones there.
Probably Poseidon, as he is Percy's father and has a vested interest in his son's well - being. Zeus might also be protective in some cases, despite their past differences, as Percy is a hero who often saves the world which benefits Zeus's realm as well.
In some versions, Neville could also be one of Harry's protective mates. Neville, who grows in courage throughout the series, would be willing to stand up against any threat to Harry. And Luna, with her unique perspective and magical abilities, might also be part of Harry's protective group.
Their shared experiences play a big role. They've been through so much together, like countless battles and adventures. Percy has seen Annabeth in tough situations and he knows how strong she is, but also how vulnerable. So he feels the need to protect her. For instance, they might have had a close call in a previous adventure where Annabeth was nearly killed, and that memory makes Percy extra vigilant.
Perhaps Anko has a personal connection to Naruto. Maybe she sees a bit of herself in him, like his determination in the face of difficulties, and this makes her feel a sense of kinship and thus the need to protect him.
One reason could be that he sees Naruto as a younger version of himself in some ways. Both have had their share of loneliness and challenges growing up. Kakashi may want to prevent Naruto from going through the same pain he did. Another reason is Naruto's importance to the village. As the jinchuriki of the Nine - Tails, Naruto is a key asset. Kakashi, being a loyal ninja, wants to protect the village's future which is tied to Naruto.
Well, it could be that in the fanfiction's plot, Harry has some special qualities or is in a dangerous situation. Edward, being a character with his own set of values, decides to be protective. For example, if Harry has some sort of power that others might want to misuse, Edward would step in to safeguard him. It might also be related to their shared experiences or a bond that has developed between them over the course of the story.