It could be that James has some ideas about dealing with certain characters or situations that Harry thinks are wrong. For instance, James might want to approach a dark wizard in a more aggressive and unplanned way, but Harry, who has faced many challenges, knows the importance of strategy and caution, thus he doesn't agree.
Maybe Harry has different values. For example, James might be more reckless in his actions, while Harry, having grown up with different experiences, is more cautious. So this difference in attitude towards things could lead to his disagreement.
The fanfiction could develop the conflict by showing how their different beliefs affect their relationships with other characters. If James is friends with a group that Harry doesn't trust, it can intensify the disagreement between them. As they interact more with these different groups, the conflict grows.
Perhaps they are blackmailed. A powerful dark wizard could threaten to harm all of their friends and family if they don't abandon Harry. They may feel they have no choice but to sacrifice their relationship with their son to protect others they care about.
It might be related to power dynamics. If in the fanfiction, James has a lot of power and misuses it in a way that affects Harry or those around him, Harry would hate him. For example, if James uses his influence to push through unfair rules or to marginalize certain groups that Harry supports. Also, if the fanfiction changes James's personality to be more self - centered and less empathetic, Harry would likely dislike him.
One possible reason could be an alternate universe scenario. Maybe in that fanfic's universe, there are dark forces at play that make Lily and James act out of character and ignore Harry. It could also be a plot device to create a more angsty or dramatic story, where Harry has to face challenges without the support of his parents.
One reason could be the hero - centric nature. Just as James Bond is the central figure in his adventures, Harry Potter is the focus in his own story. They both embark on dangerous quests and have to outwit their enemies. Another reason might be the element of secrecy. Bond has his spy secrets, and in Harry Potter, there are many secrets within Hogwarts and about the wizarding world.
One possible reason could be their fundamental differences in personality. Harry is brave and impulsive at times, while Snape is often brooding and secretive. Their past interactions, which were mostly filled with animosity and mistrust, could also be a factor. Harry might not be able to see Snape in a romantic light due to all the times Snape was cruel to him in school.
An ancient dark magic entity that has a vendetta against the Potter bloodline. It targets Harry and James, and they have to uncover the secrets of their family's past to defeat it. This antagonist could bring in a lot of mystery and exploration of the Potter family history.
One possible reason could be that Dean is better at something that Harry secretly wishes he was good at. For example, if Dean is really popular among their peers and Harry feels overshadowed. Another reason might be related to a girl they both like. Maybe the girl shows more interest in Dean, and Harry can't help but feel jealous.
One reason could be for the sake of novelty. Fanfic writers like to create unique and unexpected scenarios, and this is a very different take on the Potter family. It grabs readers' attention.
Perhaps James has more resources to take care of Harry. He could have a better living situation, more financial stability, or a stronger support system. In fanfiction, this can be a way to create a new dynamic for the characters, with James being the sole provider and protector for Harry.