One possible scenario could be that Ginny and Harry are in the Gryffindor common room. Ginny has had a long day of Quidditch practice and studying. She sits next to Harry on the couch, and as they are chatting softly about their day, her eyes start to droop. Harry notices but doesn't want to disturb her, and soon she falls asleep on his shoulder. Harry then just sits there, feeling a warm sense of protectiveness and contentment.
In a fanfic, it could be after a battle. Ginny has fought bravely but is exhausted. Harry and Ginny find a quiet corner in the rebuilt Hogwarts. They sit down, and Ginny's adrenaline rush is wearing off. She rests her head on Harry's lap and falls asleep. Harry strokes her hair gently, thinking about how lucky he is to have her by his side through all the tough times.
Maybe they are on a Hogwarts Express journey. Ginny is tired from all the excitement of the start of a new term. She leans against Harry as they are sitting in a compartment together. The gentle rocking of the train lulls her to sleep. Harry smiles to himself, remembering all the times they've shared and how much she means to him. He quietly takes out a book to read while she sleeps.
One possible scenario could be that Harry finally finds the courage during a quiet moment at Hogwarts, perhaps in the Gryffindor common room by the fireplace. He might stutter a bit at first, but then clearly say his feelings. Another could be that it happens during a dangerous adventure when he realizes he can't hold his feelings in any longer, fearing he might lose Ginny. Maybe he confesses after Ginny has been in some sort of danger and he realizes how much she means to him.
The relationship can be shown as one of deep trust. Ginny feeling comfortable enough to fall asleep on Harry indicates she trusts him completely. It could also show a sense of intimacy, like they are in a very close and personal space.
One popular scenario could be after a long day of studying in the library. They might be researching some ancient magic together, and Draco, exhausted from the mental strain, dozes off on Harry. Another might be during a truce in the middle of a wizarding war. They find a moment of peace in a hidden corner, and Draco, feeling a sense of safety for once, falls asleep beside Harry. There could also be a situation where they are on a magical journey, perhaps searching for a lost magical artifact. The journey tires Draco out and he falls asleep on Harry as they take a break in a forest clearing.
A great scenario in a Ginny and Harry get married fanfic would be a destination wedding in a far - flung magical place. Maybe they choose a wizarding island where they can have the ceremony on the beach under a starlit sky filled with magical constellations. Another scenario could be that they get married in a rebuilt Hogwarts, with the castle being a symbol of their past and their future together. And then there could be a scenario where Ginny and Harry have a very modern - wizarding wedding, with new spells and charms being used for the decorations and entertainment that no one has seen before.
One possible scenario could be that they are in the Gryffindor common room. The fire is crackling, and everyone else has gone to bed. Harry and Ginny sit on the couch, and slowly start to get closer. Their eyes meet, and then they share a gentle kiss that gradually becomes more passionate as they let their feelings for each other take over.
One possible scenario could be that Ginny meets an old acquaintance who has changed a great deal and she starts to have feelings for this person while still being with Harry. Maybe they share a common interest that she feels Harry doesn't understand. However, this goes against Ginny's strong character in the original series, so it's a very different take in fanfiction.
In some versions, it could be that Harry has to die to break a dark curse placed on Ginny. He discovers that his life is the key to saving her and willingly gives it up. He might have a premonition about Ginny's fate and decides that his death is the only way to change it. He then confronts the source of the curse and allows it to take his life instead of Ginny's.
One possibility is that they've had a long and tiring adventure. After facing numerous challenges, they find a moment of peace and Annabeth, exhausted, falls asleep on Percy. It could also be a sign of their deep trust in each other. In fanfiction, this might be used to show the closeness of their relationship.
One possible scenario could be Sirius noticing how Harry blushes whenever Ginny's name is mentioned. So he might say something like, 'Harry, I've seen you go redder than a Weasley's hair at the mention of Ginny.' Another could be if Ginny gives Harry a special gift, and Sirius teases him about it, 'Harry, that little present from Ginny must mean something special, eh?' A third scenario could be when Ginny is around and Harry acts a bit clumsy. Sirius would then joke, 'Harry, you're more out of sorts than a drunk Hippogriff when Ginny's near.'
In some fanfictions, Harry and Ginny might fight side by side, using their respective magical skills. Ginny could be shown as a fierce fighter, using her Bat - Bogey Hex to great effect against the enemies, while Harry uses his Patronus to protect them from Dementors if any are present during the battle.