One way to develop their relationship is through a magical accident. Suppose a spell backfires and links their minds in some way. Now they can experience each other's memories and emotions. Harry experiences Tom's difficult childhood, which makes him more sympathetic. Tom, on the other hand, gets a glimpse of Harry's future and the destruction he causes as Voldemort. This shared experience could be the starting point for a complex relationship where they both try to change the future and the past. They might argue, they might cooperate, but through it all, they are constantly learning about each other and themselves.
At first, it might be rocky. Tom would be suspicious of Harry's intentions. But as Harry shows him genuine care, Tom would start to open up. Eventually, they could become like family, with Tom looking up to Harry as a role model.
One unique way is through a shared secret. For example, Fem Harry discovers a hidden part of Hogwarts that is related to a powerful and ancient magic. Tom Riddle also stumbles upon this secret. Instead of fighting over it, they decide to explore it together. During this process, they rely on each other's skills and knowledge. This shared adventure builds a deep bond between them, and they start to see each other in a new light, far from their initial impressions.
As the story progresses, their relationship could become more complex. Harry might become a father figure to Tom, teaching him right from wrong. Tom, on the other hand, could start to see Harry as someone he can rely on, but also struggle with his own inner demons that might pull him away from Harry's influence.
They could start by having small moments of understanding. For example, when one of them is in trouble, the other shows unexpected kindness. This could gradually build trust between them.
Well, in some fanfictions, Tom Riddle could be developed as having a bit of a conscience from the start. Maybe the diary contains some part of his soul that wasn't fully corrupted yet. So instead of being purely evil, he has moments of hesitation or confusion about his actions.
Well, in some fanfics, the relationship is depicted as a strange sort of friendship. They find common ground in their love for magic knowledge. However, there are also fanfics where Tom Riddle is obsessed with Harry Potter from the start, not just as an enemy but in a more psychological way. He sees Harry as a symbol of everything he could have been if he had made different choices.
Well, in some fanfics, their relationship can be portrayed as a mentor - mentee relationship in reverse. Instead of Dumbledore mentoring Harry, Harry could try to mentor the young Tom Riddle. Harry would use his own experiences of overcoming darkness to guide Riddle away from the path of evil.
It could also develop through a series of challenges. Say there are magical trials within the locket's magic. Harry and the Tom - essence have to face these trials together. As they overcome each obstacle, they learn more about each other's strengths and weaknesses, and their relationship grows from mutual respect in the face of danger.
At first, it would probably be really tense. Tom is used to being on his own and having his own dark thoughts. Harry would be super cautious. But as time goes on, Harry's kindness might start to break through Tom's barriers. They could become like brothers, with Harry teaching Tom about the good in the world and Tom starting to trust Harry.
For Harry, his sense of justice and determination can be explored further. He might struggle with his feelings towards Tom as it goes against what he has always known about Voldemort. Tom, on the other hand, his intelligence and ambition can be shown in a new light. Maybe he is conflicted between his dark desires and the positive influence Harry has on him.