It could also be that Harry and Draco have developed an unexpected friendship in this fanfiction. Harry feels protective of his friend and doesn't want Draco to be uncomfortable around the girls. So he uses his influence or just his physical presence to keep the girls at bay.
Maybe Harry has seen how some of these girls can be really pushy and it could potentially harm Draco in some way, like ruining his reputation or causing him emotional distress. Harry, being the hero type, steps in to protect Draco from that.
One reason could be that Harry has a newfound sense of fairness. He realizes that Draco is constantly hounded by over - eager girls and he doesn't think it's right. Harry has been through a lot himself and he might empathize with Draco not wanting to be bothered all the time.
He might simply stand between Draco and the girls. Harry is quite well - known and respected, so his presence alone could be enough to make the girls back off a bit.
One possible reason could be that Draco has had a change of heart. Maybe he realizes that Hermione is a person worthy of protection regardless of her House or her friendship with Ron. He might have seen some injustice about to befall her from Ron and his Gryffindor bravado getting out of hand.
One of the main challenges could be the animosity between Gryffindor and Slytherin. Harry is a Gryffindor and Draco is a Slytherin, and their houses have a long - standing rivalry. So, other students from both houses might not understand why Harry is protecting Draco and could try to interfere. Another challenge could be Draco's own pride. He might not want to be seen as needing protection, especially from Harry, which could make it difficult for Harry to do his job. Also, there could be external threats, like dark wizards who target Draco for some reason, and Harry has to constantly be on guard against them.
One common scenario is in a dangerous magical situation. For example, in a battle at Hogwarts, Draco might step in to protect Harry from a dark wizard's spell. Another could be in the face of social threats within the school. Maybe some students are trying to bully Harry, and Draco, having a change of heart, defends him. It could also be that Draco protects Harry from a plot within the Slytherin house that aims to harm Harry due to his fame as 'The Boy Who Lived'.
One common theme is redemption. Draco is often seen as a character who needs to be redeemed, and Harry's protection plays a part in that. For example, Harry's actions can make Draco realize there's more to life than following the dark path.
One popular 'Draco protects Harry' fanfic is 'The Green Serpent' where Draco's hidden loyalties lead him to safeguard Harry in the face of dark forces at Hogwarts. Another could be 'Draco's Redemption' which shows Draco's transformation and his determination to keep Harry out of danger. There are also many on Archive of Our Own (AO3) under the 'Draco/Harry' relationship tag that explore this theme.
One common reason could be his love for Lily. Since Harry is Lily's son, Snape might feel an obligation to protect him out of his undying love for her. It's like he's trying to preserve a part of Lily that still exists in the world through Harry.
Well, Harry might save Daphne from Draco because Harry is always the hero type. He doesn't like Draco's pure - blood supremacist attitude. Daphne could be a target of Draco's cruel remarks or actions just because she might not fully conform to Draco's ideas. Harry, being the defender of the underdog in many cases, steps in. Also, it could be that the plot of the fanfiction is building a new alliance or relationship web, and Harry saving Daphne is a key part of that, leading to new story developments.
One popular 'harry protects draco fanfiction' is 'The Protector'. In this fic, Harry realizes Draco's not as bad as he seems and starts to protect him from the real threats in the wizarding world. It has some really great character development.
In many cases, the main antagonists can be other Slytherins who still hold grudges against Harry or are loyal to the pure - blood supremacist ideology. They might see Harry as a threat to their way of life. Also, some Death Eaters can be antagonists. They target Harry because of his role in Voldemort's downfall and would stop at nothing to get to him.