One way is if they are both chosen for a secret mission by Dumbledore. He believes that their combined abilities and different perspectives can be useful. At first, they are reluctant to work together. But as they face various challenges during the mission, like navigating through a dangerous enchanted forest or deciphering ancient runes, they realize that they complement each other well. Harry's ability to think on his feet and Draco's knowledge of Slytherin - related magic and lore make them a great team. This experience changes their relationship from one of enmity to a grudging friendship.
Their relationship could develop through a shared love of potions. Harry discovers he has a natural talent for it, much to Snape's surprise. Draco, being a traditional Slytherin, also excels in potions. They start to compete in a friendly way, which then turns into a mutual respect for each other's skills. This could lead to them working together on a special potion project that requires both Gryffindor - like boldness (from Harry) and Slytherin cunning (from Draco).
Their relationship could develop uniquely if Malfoy were to see Snape's vulnerable side. For example, Snape might have a moment of weakness after a particularly difficult encounter with the Order of the Phoenix. Malfoy, instead of using it against him, could show empathy, which would change the dynamic between them.
In the fanfiction, their relationship could be developed uniquely if Fem Harry Potter is from a different magical culture. James Potter is intrigued by her different ways of using magic and her cultural beliefs. They start to exchange knowledge and through this, a relationship blossoms. James helps her adapt to the Hogwarts way of life while she broadens his perspective on magic in general, and they become very close as a result.
Their relationship could develop through a shared love of a particular magical creature. For example, they both discover a new, endangered magical creature and have to work together to protect it. This shared mission could bring them closer.
Their relationships could be developed uniquely by having them participate in a magical tournament that's not like the Triwizard Tournament. They are on different teams but have to cooperate secretly to overcome some corrupt judges. Draco might start to see Harry and Hermione in a new light as they work together to expose the wrongdoings. This shared experience outside of the normal Hogwarts rivalries can bring them closer.
In a fanfiction, their relationship could develop through a shared struggle. For example, if there was a new dark force emerging that threatened both the old and new wizarding order. Abraxas, with his experience, and Harry, with his courage, would be forced to team up. Along the way, they would learn about each other's values. Harry might see that Abraxas wasn't all about pure - blood supremacy but had his own code of honor. Abraxas would see Harry as more than just a Gryffindor upstart and recognize his leadership qualities.
If Lavender was cursed in some way that made her forget her memories of Hogwarts, Harry could be the one to help her regain them. He would take her around the castle, showing her familiar places and telling her stories of their time together. As she slowly starts to remember, she begins to see Harry in a new light. This process of rediscovery could lead to a deep and emotional connection between them, as they are basically rebuilding their relationship from scratch. And it would also show Harry's caring side towards someone who wasn't necessarily in his inner circle before.
At first, it might be less hostile. Since they're in the same house, Draco might see Harry as someone he can influence or befriend. Harry, on the other hand, would be cautious but also curious. They could end up having a sort of begrudging respect for each other as they realize they both have complex personalities.
In some fanfictions, it could develop due to a common enemy. Maybe there's a new dark force emerging in Hogwarts, and they both realize that they need to put aside their differences to face it. This shared goal makes them rely on each other more, and feelings start to grow as they see the other's courage and determination. Their relationship could grow from a begrudging alliance to a full - fledged romance as they discover new sides of each other.
Suppose there's a Tri - Wizard Tournament - like event at Hogwarts. Harry's sister and Draco are both chosen as representatives for their houses. They are forced to train together. At first, they are constantly bickering, but as they face the challenges together, they learn to trust and rely on each other. This shared experience could be the foundation for a deeper relationship.
The relationship could develop uniquely if Fem Harry Potter uses her empathy skills. Since she is different from the original Harry, she might be more in tune with Bellatrix's pain and past traumas. For example, if she discovers that Bellatrix was once a victim of dark magic herself which led her to become a Death Eater, Fem Harry Potter could try to heal her. This would create a very different dynamic compared to the usual enmity between Harry and Bellatrix.