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.
A third scenario could be jealousy. If other witches start showing interest in Harry and he doesn't immediately and firmly shut it down, Ginny might get mad. She is a proud witch and doesn't want to share Harry's affections, and his seeming indecisiveness in such situations could lead to her anger in fanfiction.
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 them simply having a picnic by the lake near Hogwarts. They talk about their future, like Ginny planning to play Quidditch professionally and Harry thinking about becoming an Auror. They laugh at how normal it all feels after the chaos of the war.
Rebuilding. After the war, not only do they rebuild their relationship, but often in these stories, they are also involved in rebuilding the wizarding world. Like helping to repair Hogwarts or restoring the trust among the wizarding community.
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.
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.
In such a fanfiction, Harry might initially struggle with his blindness. Ginny, being the strong - willed character she is, would encourage him to not let it hold him back. There could be a lot of emotional moments between them, like when Harry first realizes he can no longer see Ginny's beautiful face. Ginny, on the other hand, would assure him that their love is not based on sight. They might also encounter difficulties from the wizarding society that doesn't fully understand how to deal with a war - hero - turned - disabled, but they would face it all together.
They might get married and start a family right away. In fanfiction, it's common to see them settling down and having kids, living a peaceful life after all the chaos of the battle.
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.