Some fanfictions have a plotline where they form a secret club or group. They might be working against a new threat that the official Hogwarts authorities are not aware of. It shows their loyalty to each other and their ability to take matters into their own hands to protect the wizarding world.
One interesting plotline could be Harry and Luna raising their children in a magical world filled with new and strange creatures. Their kids might inherit a unique blend of their parents' traits, like Harry's bravery and Luna's eccentricity.
One possible plotline could be Ginny being influenced by a dark magical object that makes her turn against Harry. This could lead to a series of conflicts as Harry tries to figure out what's wrong with her and how to save her. Another plotline might involve Harry and Ginny being caught in a dark prophecy that forces them to make difficult choices that seem against their nature. For example, they might have to choose between saving each other or the wizarding world.
One interesting plotline could be the paparazzi misinterpreting a friendly moment between Harry and Ginny as something more romantic, which then causes chaos in their wizarding world. For example, they might take a picture of Harry helping Ginny up after she falls during Quidditch practice and spin it into a love affair story.
One interesting plotline could be how Harry and Ginny handle their kids' magical education. For example, they might have different ideas on whether to send them to Hogwarts early or let them study at home for a while first. Another could be the family's adventures during holidays, like exploring new magical places together.
One interesting plotline could be their post - war life. How they deal with the trauma of the war and build a normal life together. For example, they might struggle with nightmares but find comfort in each other.
One interesting plotline could be Harry and Ginny having a secret date in Hogsmeade. They might discover a hidden alley with a magical shop that holds a key to solving a mystery at Hogwarts. Another could be that they encounter a strange creature near Hogsmeade and have to work together to keep it from causing chaos in the village. And also, perhaps they meet an old wizard in Hogsmeade who tells them a prophecy about their future together.
Well, in some 'harry and ginny unexpected fanfiction', there could be a plot where Harry and Ginny accidentally swap their magical abilities. This would lead to a lot of comical and also challenging situations. For example, Ginny would have to deal with Harry's fame while Harry would have to adjust to Ginny's more personal relationships within the school. Also, there might be a story where they find a hidden chamber in Hogwarts that has a connection to their future together. Maybe it shows them visions of their possible lives and they have to decide how to make those visions a reality.
One interesting plotline could be Luna and Harry getting to know each other better during the Yule Ball preparations. Maybe they discover a shared love for some strange magical creatures while practicing their dance steps.
In some fanfictions, a great plotline could be Harry and Luna forming a closer bond because of the Goblet of Fire chaos. Luna could be the one to comfort Harry when he's facing the difficulties and dangers of the tasks. And together, they might even uncover a conspiracy among the teachers or judges that was meant to manipulate the results of the Triwizard Tournament.
One interesting plotline could be that Harry and Luna travel back in time to prevent the death of Sirius Black. They might use their knowledge of future events to outwit Voldemort's minions and change the course of that tragic event.