In this fanfiction, it could be that Sirius helps Harry train his Patronus more effectively. Since Sirius has his own experience with Dementors, he could teach Harry advanced techniques. They might also encounter a large number of Dementors sent by Voldemort's followers. Harry's improved Patronus skills, with Sirius' guidance, would be crucial in warding them off and protecting their home and the surrounding wizarding community.
Perhaps there could be a plot where Sirius and Harry team up to uncover secrets about the Dark Arts that are hidden in the Black family home. As they explore the old rooms and artifacts, they might stumble upon a powerful and dangerous object that the Death Eaters are also after. This would lead to a race against time to either destroy or protect the object while also fending off the Death Eaters.
One possible plot development could be that Harry finally experiences a true family environment. Sirius could teach Harry more about his parents, their secrets, and the wizarding world in a more personal way. They might also face some threats together as Sirius is still a wanted man in some parts of the wizarding world. This would create a lot of tension and action scenes in the fanfiction.
It could be about Sirius teaching Harry advanced magic skills like Patronus charm. Sirius, being a skilled wizard, might train Harry to be better at dueling and facing dark wizards.
One possible plot could be that Harry and Sirius are somehow transported to the world of Game of Thrones. Harry could use his magic skills to survive in the cut - throat world, while Sirius, with his werewolf - like abilities (from being an Animagus), could be a fearsome fighter. They might get involved in the power struggles between the different houses, perhaps siding with the Starks as they are known for their honor. They could use their knowledge from the wizarding world to introduce new concepts like magic (though it might be seen as sorcery in that world) and change the course of the wars in Westeros.
One possible plot could be that Harry, after years of dealing with the chaos in the wizarding world, decides to live by himself to find inner peace. He might choose a secluded place, like a small cottage deep in the Forbidden Forest. He spends his days studying ancient magic that he never had time for before, and perhaps he starts to document his past adventures in a detailed journal.
One possible plot could be that Harry and Fleur end up living together due to some post - war arrangements. They might initially have a bit of a cultural clash as Fleur is part - Veela and has her own French - influenced ways, while Harry is very much a product of the British wizarding world. But over time, they learn from each other and become friends. Harry could be teaching Fleur about some of the more unique aspects of Hogwarts' history that she might not know, and Fleur could be showing Harry some of the beautiful magic she learned in Beauxbatons.
Perhaps they live together because they both feel a bit out of place in the regular Gryffindor dormitory. They start a little project where they try to combine their magical skills. Harry's talent for Defense Against the Dark Arts and Neville's growing confidence in his own magic could lead to them developing new spells or magical techniques. They might also have a shared garden where Neville grows magical plants and Harry helps protect them from dark creatures that might be attracted to the powerful magic of the plants.
One possible reason could be Sirius believing he can protect Harry better on his own. Maybe he thinks the Dursleys are too dangerous for Harry and that the wizarding world isn't doing enough. So, he decides to take matters into his own hands and kidnap Harry to keep him safe.
Well, perhaps Sirius trains Harry in advanced defensive magic. Harry could learn spells like the Patronus charm more effectively under Sirius's tutelage. Sirius might also teach Harry about the wizarding world's secrets that Dumbledore didn't share.
One possible plot could be that Harry and Sirius' daughter grow up together. They might start as friends, sharing adventures at Hogwarts. As they get older, they realize their feelings for each other are more than just friendship. Harry, being the hero he is, would be very protective of her. Their relationship could face challenges like dealing with the memories of Sirius and the expectations of the wizarding world. Maybe they have to fight off some dark forces together which makes their bond even stronger, leading to their marriage.
Well, perhaps they begin by magically cleaning the flat first. After that, they might decide to put up some pictures on the walls. Sirius could bring out some old photos of Harry's parents that he's been saving. They also might use some spells to create floating candles for a cool lighting effect. And they could make a cozy corner with a big, plush armchair and a bookshelf filled with Harry's favorite books.