It could be that they are on a mission together and get poisoned by some magical substance that has the side effect of making them drunk. In their inebriated state, they start reminiscing about their past, from their first meetings to their first kisses. This trip down memory lane makes them realize how much they truly love each other and how far they've come as a couple.
One possible plot could be that Harry is under the influence of a dark spell. In this state, he kidnaps Ginny because the spell is making him act against his true nature. Ginny, being the strong - willed character she is, tries to break through to Harry and reverse the spell's effect on him.
One possible plot twist could be that while drunk, they accidentally reveal secrets they've been keeping from each other. For example, Ginny might let slip about a small insecurity she has in their relationship that she's been hiding. Another could be that they end up in a part of Hogwarts they've never been to before while drunk and discover something mysterious, like an old hidden room with strange artifacts. Maybe they also get into a bit of trouble with the school authorities when they are found drunk, but this incident actually brings them closer as they face the consequences together.
One possible plot could be that they initially panic. Harry might worry about being able to protect his new family while Ginny would be thinking about how this would change their lives. They could face reactions from their friends and family, some being supportive and others expressing concern. Then they start to prepare for the baby, like finding a new place to live that's more suitable for a family.
In such a fanfic, perhaps Ginny has been feeling neglected by Harry due to his constant focus on fighting dark forces or some other important matters. So she starts to seek comfort in someone else. When Harry finds out, he first feels angry and betrayed. But then he realizes that he also had a part to play in their relationship going sour. He could then try to win Ginny back or decide to move on, depending on how the author wants to develop the story.
Maybe Ginny gets a fever after being exposed to a dangerous magical artifact. The fever makes her have strange dreams. Harry, being the hero, tries to enter her dreams to figure out what's wrong. He battles the dark forces within her dreams and finally manages to wake her up and cure her fever.
Well, one possible plot could be their daily adventures in raising their children. Maybe they face some magical challenges in protecting their family from dark forces that still lurk in the wizarding world. They could also be involved in rebuilding Hogwarts and passing on their magical knowledge to the new generation.
Well, it could start with Harry nervously asking Ginny to meet him at the Hogwarts grounds. Maybe they go for a walk by the lake, holding hands and sharing stories. They could end up at the Astronomy Tower, looking at the stars and having a really deep conversation about their future together.
Well, perhaps the fanfic could focus on their travels. They decide to explore different parts of the wizarding world that they haven't seen before. Along the way, they encounter old friends and new magical creatures. And they also have to deal with some dark wizards who are still causing trouble after the war.
One possible plot could be a detailed account of their wedding day. It might start with Ginny waking up, feeling a mix of excitement and nervousness. Harry could be shown getting ready with Ron and Hermione by his side, sharing some old memories. The ceremony could be a grand affair with all their friends and family from Hogwarts present. There could be a magical display during the vows, perhaps some floating candles and enchanted flowers. After the wedding, they could have a reception filled with dancing and laughter, and then they might go on a honeymoon to a secret, magical location.
It could be that Ginny uses a dark magic spell in a moment of anger or recklessness. Harry, being the defender of the light, punishes her by making her study the history of the harm caused by dark magic. As she delves into this study, she realizes the error of her ways and has to work hard to regain Harry's trust. This could involve her doing community service within the wizarding community related to those who have been affected by dark magic.