Well, Sirius might see some of his own qualities in Harry's boyfriend. Maybe the boyfriend is brave like Sirius was, and Sirius would then start to warm up to him. He could share some of his old Hogwarts stories with the boyfriend, which would help the boyfriend understand Harry's world better.
It could be Draco Malfoy. In some fanfictions, they put aside their differences and develop a relationship. Sirius would be very surprised as he used to see Draco as an enemy. But seeing Draco's growth and his love for Harry could change Sirius' view.
Well, Sirius might be shocked by the Dursleys' treatment of Harry. He could try to rescue Harry from their mean ways.
In a fanfiction where Petunia meets Sirius, it could be a very interesting encounter. Sirius, being a wizard from the wizarding world, might shock Petunia at first. He could show her some simple magic, like making a flower bloom, which would both terrify and fascinate her.
If it's a fanfiction about Class 1A meeting Bakugou's boyfriend, there could be a lot of comical moments. Maybe Mineta would try to be inappropriate and get scolded by Bakugou. The more responsible students like Iida might give Bakugou relationship advice. His boyfriend could be from another class or even another school. If he's from another school, Class 1A would be curious about the differences in their hero training. And Bakugou would have to balance his relationship with his training and his place in Class 1A.
One possibility is that their meeting is a vision or a dream - like encounter. Harry could be drawn into Azkaban in his sleep or through a magical object. During this encounter, Sirius could give Harry advice on how to deal with the upcoming challenges at Hogwarts. He might warn Harry about certain people who can't be trusted and offer his insights on the growing dark forces.
Perhaps Sirius will be overawed by Remus' parents' love for their son. He might compare it to his own family situation and feel a bit envious. On the other hand, Remus' parents might see Sirius as a broken soul in need of love and acceptance. This could lead to a very heart - warming relationship where they take Sirius under their wing and help him become a better person while also fully accepting his relationship with Remus.
In this fanfiction, perhaps James Sirius Potter could learn some of the classic pranks the Marauders were famous for. He might get into all sorts of adventures, following in their footsteps and causing a bit of chaos at Hogwarts just like they did.
In the fanfiction, they might have a heartfelt reunion. They could share all the things they didn't get to say before. Maybe they'd talk about their friends left behind, like Remus and Harry. They'd probably also recall their adventures at Hogwarts, from the pranks they played to the battles they fought together.
Well, perhaps Klaus will initially be skeptical of Landon as Hope's boyfriend. He might test Landon's loyalty and strength. Maybe there'll be some tense moments where Klaus's protective nature for Hope clashes with Landon's attempts to prove himself worthy of her.
Well, perhaps Harry has a really heart - warming conversation with the Grangers. He could share his wizarding world experiences with them, and they might be super fascinated.