In some fanfictions, misunderstandings can lead to one character hurting another. So, Ginny might misunderstand Harry's intentions. For instance, she sees him talking secretly with an old flame and jumps to the wrong conclusion. In her anger and hurt, she decides to get back at him. She could spread false rumors about Harry around Hogwarts, which would hurt his reputation and also his feelings deeply.
One possible plotline could be that Ginny accidentally hurts Harry during a Quidditch match. Maybe she's trying to catch the Snitch and doesn't see Harry in her way, and her broom collides with his, causing him some physical pain. Another could be an argument where Ginny says some harsh words that emotionally hurt Harry. For example, if she's jealous of his friendship with Hermione and lashes out at him, saying things like he doesn't really care about her as much as he does Hermione.
Betrayal is a common theme. Ginny might betray Harry's trust in some way, like revealing a secret he told her in confidence. This would cause him a great deal of emotional pain. Another theme could be jealousy. If Ginny is jealous of Harry's relationship with someone else, she could act out in ways that hurt him.
One possible plotline could be Harry and Ginny facing new magical threats in Hogwarts during their 8th year. Maybe there are remnants of Voldemort's followers who are trying to disrupt the newfound peace. Another could be their relationship growing stronger as they deal with the challenges of post - war Hogwarts together. They might also discover new magical secrets within the castle.
Perhaps there's some external influence on Ginny. Maybe a dark magic spell was cast on her that made her have negative emotions towards Harry. In the wizarding world, there are many powerful spells that can manipulate emotions, and if Ginny was under the effect of such a spell, it could lead to her saying she hates Harry.
A plot could involve Snape's deaging being the result of a dark magic experiment gone wrong. Harry and Ginny initially suspect foul play but soon realize that Snape is truly a child in mind and body. They decide to protect him from those who might want to use his situation for their own gains. As they do so, Snape begins to form a bond with them, especially with Ginny, who he sees as a sister - like figure. Harry, meanwhile, has to deal with his own mixed feelings towards this new Snape, as he is constantly reminded of the old, often - hated Snape, yet also sees the potential for a new beginning.
One possible plotline could be that Harry is so focused on his fight against Voldemort that he doesn't have the emotional space to develop feelings for Ginny. He might see her as just a friend or even as a younger sister figure. For example, he could be constantly training, researching dark magic defenses, and leading the Dumbledore's Army, leaving no room for romantic thoughts about Ginny. Another aspect could be that Harry has unresolved trauma from his past, like the death of his parents, which makes him hesitant to get involved in a romantic relationship with Ginny.
One possible plotline is that Harry and Ginny plan a surprise for the Weasley family. They could use their magic to create a spectacular light show outside the Burrow. Another is that Ginny's old school friends come to visit during Christmas, and there's a bit of friendly rivalry between them and Harry over Ginny's attention. But in the end, it all ends with a big Christmas party where everyone has a great time.
One possible plotline could be that they disappear to escape a new dark threat that has emerged in the wizarding world. They might be seeking a powerful magical artifact to defeat this threat and have to go into hiding to find it.
One plotline could be that they secretly married to protect Ginny from a dark wizard who has a vendetta against Harry. By being secretly married, they think they can keep Ginny out of harm's way. Another could be that they did it on a whim during a romantic getaway and then decide to keep it a secret just for a while to enjoy their private time together.
Another plotline might be their family life. They could be shown starting a family early, and dealing with the joys and challenges of raising children in the wizarding world. For example, teaching their kids magic at home, or dealing with the chaos of a family full of young wizards.
One possible plotline is Teddy's education. Harry and Ginny could be very involved in Teddy's magical education. They might encourage him to study different branches of magic, like Transfiguration or Potions. Another plotline could be Teddy's relationship with his godfather, Harry. Since Harry is like a father figure to Teddy, their bond could be explored, such as how Harry imparts his values to Teddy.