A great 'Protective Percy of Harry' fanfic is 'Percy's Unwavering Shield'. In this fanfic, Percy is portrayed as a sort of guardian angel for Harry. He anticipates the threats against Harry before they even happen. He forges alliances within Hogwarts and outside to ensure Harry's safety. Percy's character is shown to be much more complex than in the original books, as his protective nature towards Harry brings out different sides of him, like his strategic thinking and his ability to manipulate situations to Harry's advantage.
There are quite a few. Some fanfics focus on individual Slytherin students who form an unlikely bond with Harry. They might protect him from the dark forces that are after him, seeing him as more than just the 'Chosen One' but as a friend in need. These fanfics often explore the idea that not all Slytherins are bad and can be quite heroic when it comes to protecting someone they believe in.
In many such fanfics, Percy uses his intelligence. For example, he might study the laws and regulations of the wizarding world thoroughly to find loopholes that can protect Harry from unjust punishments or accusations.
A popular Percy Harry Potter fanfic might be 'Percy and the Secret Alliance'. In this fic, Percy forms a secret alliance with some unexpected characters in the wizarding world. As the story unfolds, his relationship with Harry also evolves in interesting ways. Some fanfics also explore Percy's role in the fight against Voldemort. He might have some unique skills or knowledge that prove crucial in the final battle, which is an aspect that many fanfic writers like to explore.
There's also 'Sirius's Oath'. It shows Sirius making an unbreakable vow, in a way, to always protect Harry. It delves into their relationship, with Sirius teaching Harry things he never learned at Hogwarts, all while shielding him from the dark forces that are after him. It's really interesting as it also shows how Sirius's protectiveness affects Harry's growth as a wizard.
One good 'protective Percy fanfic' could be where Percy protects his friends from a new and powerful monster. For example, he might use his water - controlling abilities to create a shield against a fire - breathing beast.
In many fanfics, it's about character development. Draco starts to see Harry in a new light, beyond the Gryffindor - Slytherin rivalry. He realizes Harry's vulnerability despite his hero status, which makes him want to protect him. It also adds an interesting dynamic to their romance.
Another theme is redemption. Sirius may feel he has a lot to make up for, especially considering his past mistakes. By being protective of Harry, he's sort of redeeming himself. For example, in many fanfics, he tries to prevent Harry from making the same mistakes he did when he was younger.
One great 'Harry is protective of Ginny' fanfiction is 'The Protector's Promise'. In it, Harry is constantly on guard to keep Ginny safe from various threats at Hogwarts. Another one could be 'Harry's Watchful Eye'. It shows Harry's protectiveness in a more emotional way as he fears losing Ginny to the ongoing chaos in the wizarding world.
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.
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.