Well, perhaps Sirius would be quite amused to see Harry and Ginny together. He could start reminiscing about his own youth and the relationships he had. Sirius might also give Harry some relationship advice, like how to make sure Ginny stays safe in the dangerous times they live in. And he could even tell them some secret family stories that they hadn't known before.
One possibility is that Sirius would immediately sense the strong bond between Harry and Ginny. He might take them on a little adventure in the wizarding world, showing them hidden places that only he knows. Sirius could also confide in them about his plans for the future of the Order of the Phoenix, and how he hopes they will be involved in making the wizarding world a safer place.
In fanfiction, when Harry and Ginny meet Sirius, Sirius might offer them some sage advice on dealing with the dark forces. He could share his experiences about fighting Voldemort and his Death Eaters. Maybe he would see the potential in Ginny and encourage her to further develop her magical abilities, as he has always been supportive of Harry.
In a fanfiction scenario, they could meet in Sirius's old family home at Grimmauld Place. Harry and Ginny might be exploring the place when Sirius appears. Sirius would greet them with his characteristic charm and warmth. He'd probably offer them a drink and then start a conversation about the current state of the wizarding world, asking Harry about his progress at Hogwarts and Ginny about her experiences in the Gryffindor house.
In many fanfictions, if Harry and Ginny were caught by Sirius, Sirius might be initially protective and concerned. He could question their actions, especially if they were in a situation that seemed dangerous or inappropriate for their age. For example, if they were out after curfew or in a restricted area. Sirius might give them a stern lecture about being responsible and the importance of following rules, while also understanding their adventurous spirits as he was quite the rebel himself when he was young.
If Harry and Ginny meet the Marauders in fanfiction, it would be a moment full of emotions. Harry has always longed to know more about his father, and this would be his chance. The Marauders, on seeing Harry, might see a lot of James in him. Ginny would add a different dynamic to the group. She could be the voice of reason at times. Together, they could create new memories. For example, they might team up to play a prank on Snape's memory or something, which would be both funny and a way to pay homage to the Marauders' legacy.
One possibility is that Sirius could be initially shocked. But then, being the understanding person he is, he might give them his blessing. After all, he has seen how Harry has grown and Ginny is a great girl.
In fanfiction, when Harry and Ginny meet the Dursleys, there could be a lot of tension. The Dursleys are not fond of anything related to magic. Ginny, being a confident witch, might stand up to the Dursleys' rudeness towards Harry. Harry, on the other hand, would be in an awkward position as he has to deal with his Muggle family and his magical girlfriend at the same time. There could be some humorous exchanges as Ginny tries to understand the strange Muggle world of the Dursleys while also showing them that magic is not something to be feared.
One possibility is that Harry and Ginny could use a time - turning device to go back in time and meet James and Lily. They might share stories about Harry's life, and James and Lily could give their blessings to Harry and Ginny's relationship. Ginny could also learn some of Lily's magical tips.
One scenario could be that they meet in a time - travel situation. Harry and Ginny could be transported back in time to when Lily and James were alive. There, they would get to know each other in a different way. Harry would finally be able to have a proper conversation with his parents. They could discuss the future, the prophecy, and how Harry has changed the wizarding world. Ginny could bond with Lily over their love for Harry and their Gryffindor spirit. It would be a very emotional and magical encounter.
In some fanfictions, it could be a really awkward encounter. Harry might feel a bit of tension since he has a history with Cho and is now with Ginny. Ginny, on the other hand, could be a bit jealous or just curious about their past. Maybe Cho would be polite but still have some unspoken feelings for Harry.
It's possible that when they meet their kids, they realize that their family has a special destiny in the wizarding world. Their kids could be the key to uniting different magical communities or solving an ancient mystery. This could lead to a series of adventures where Harry and Ginny, along with their kids, embark on a journey to fulfill this destiny.
They might share a very emotional moment. Harry could finally let go of all the war - related stress and just be himself with Ginny. He might tell her about all the things he couldn't during the war, like his real fears and hopes for the future. And Ginny would be there for him, comforting him and showing her love in a more peaceful and free environment.