One possible reason could be that Harry was away a lot after the war, dealing with the aftermath and his newfound responsibilities. Ginny might have felt neglected. Maybe she expected more time together, but Harry was constantly occupied with things like helping to rebuild Hogwarts or being involved in the Ministry's new initiatives.
One scenario could be that Harry is overly protective of Ginny after the war. While it may seem like a good thing, Ginny is a strong - willed witch. If Harry starts treating her like she's fragile and tries to limit her activities, she would get angry. For example, if he doesn't let her participate in certain dangerous but important magical tasks because he's afraid she'll get hurt. Also, if there are rumors or false accusations about Harry in the post - war wizarding world, and he doesn't share them with Ginny right away, she might be mad that he didn't trust her enough to confide in her.
Harry could become an Auror, as he's always been good at fighting dark forces. Ginny, on the other hand, might continue her career in Quidditch. They would support each other's choices. Harry would cheer for Ginny at her matches, and Ginny would be proud of Harry for his work in keeping the wizarding world safe.
One possible story could be that after the war, Harry suffers from paraplegia due to some dark magic he endured during the final battle. Ginny stays by his side, being his strength. She helps him through the difficult process of physical therapy. Their love becomes even deeper as they face this new challenge together.
Some fanfictions might depict them as having a more adventurous post - war life. They could be involved in rebuilding the wizarding world in a more hands - on way. Harry might use his fame and Ginny her popularity among the younger wizards to bring about positive changes. Their relationship would be based on mutual respect and a shared goal of making the wizarding world a better place.
In some fanfictions, Ginny might be mad at Harry because of a misunderstanding. For example, she could misinterpret his actions towards another girl as being unfaithful. Maybe he spends a lot of time with Hermione on a project and Ginny thinks there's something more between them.
One aspect that's often shown in fanfiction is how they help each other heal from the traumas of the war. Ginny, being a strong - willed witch, supports Harry in dealing with his post - war nightmares and insecurities. Harry, in turn, encourages Ginny to pursue her dreams in the new wizarding world. Their relationship is filled with mutual understanding, love, and respect.
It could be due to jealousy. Perhaps Ginny has been spending a lot of time with another character, and Harry misinterprets their relationship, leading to his anger. In fanfiction, the writers often play with such emotions to create drama.
Ginny would also support Harry by involving him in her own life. She'd share her dreams, her daily experiences at work or with friends. This would make Harry feel like he was still an important part of her world and not just someone she was taking care of. She might even try to find magical solutions to his condition, perhaps researching ancient spells or potions that could potentially help him regain some mobility.