The relationship could develop through shared interests. Say they both have a passion for ancient magic. They start discussing it in the library, and as they do, they find themselves drawn to each other more and more. Their conversations grow deeper, and before long, they realize they're in love. Harry might share his experiences with Voldemort with Daphne, and Daphne could open up about her family's expectations. This mutual sharing of personal and difficult things would strengthen their bond.
It could develop into a strong friendship. Since they meet as babies, they grow up with a sense of familiarity. They might trust each other more than others and always be there for one another.
In some fanfictions, their relationship develops through shared secrets. Daphne might share some Slytherin secrets with Harry, and in return, Harry tells her about his experiences with Voldemort. This sharing of personal and important information brings them closer together. They start to rely on each other more and more, and eventually, their relationship can range from a deep friendship to a romantic one, depending on the direction of the fanfiction.
In the fanfiction, their relationship could develop in a rather unexpected way. Since they live together, they are constantly in each other's presence. Harry might start to teach Daphne some of his Quidditch moves in the backyard, and Daphne could introduce Harry to some of the more sophisticated Slytherin social etiquette. As they engage in these activities together, they start to respect and admire each other more. Eventually, this could lead to a romantic relationship or a very deep friendship depending on how the author wants to take the story.
Their relationship could develop as a partnership based on mutual curiosity. Harry's Sharingan is a mystery, and Daphne's eagerness to understand unusual magic brings them together. They might start as friends, sharing their knowledge and experiences, and gradually grow closer as they face challenges related to the Sharingan in the wizarding world.
It could develop as they face challenges together. For example, when dealing with school bullies, they support each other and their bond deepens. Their relationship might also change as they start to have different views on magic and the wizarding world, but they still respect each other.
Another way is through shared interests. They might all be interested in a particular area of magic, like ancient runes or potions. As they explore this interest together, they learn more about each other's values and beliefs. This mutual understanding helps their relationship to grow and evolve, and they become close friends who support each other through various challenges in the wizarding world.
They could become study partners. Since they meet on the train, they might realize they can help each other out in different subjects at Hogwarts.
In this fanfic, Harry would likely grow in his social skills. Since Daphne has different social circles, he'd be introduced to new people and ways of interacting. He might become more diplomatic, learning from Daphne how to handle different personalities gracefully. Daphne would develop a stronger sense of loyalty. As she gets to know Harry better, she'd see his unwavering loyalty to his friends and causes, and this would inspire her. She might also become more adventurous, as Harry often gets into exciting (and sometimes dangerous) situations, and she'd be drawn into them, expanding her own boundaries.
They would likely become closer. Having a baby is a big responsibility, and they would need to rely on each other more. Their relationship might shift from a more romantic and carefree one to a more mature and partnership - based one, focused on the well - being of their child.
Their relationship could lead to more unity in the wizarding world. Since Harry is a well - known figure and Daphne is from a Slytherin family, their friendship might break down some of the traditional barriers between Gryffindor and Slytherin. It could inspire other students to look beyond house rivalries and work together for the greater good.