A plotline could be that Harry, after being dumped by his parents, has a very different personality. He's more withdrawn and distrustful. Sirius has to work hard to break through those walls. They could travel to different magical places to find a way to reverse what Harry's parents did or to find out the real reason behind it. Along the way, they meet other characters who either help or hinder their journey, and this all shapes their relationship and Harry's growth as a person.
A third plotline might be that Harry is abandoned in a magical but hidden place. There, he is raised by magical creatures, say, a group of centaurs. They teach him their own brand of magic and wisdom. When he finally enters the wizarding world proper, he has a very different perspective on magic compared to the other students, which causes both admiration and some envy among his peers.
One possible plotline could be Harry growing up in an orphanage where he discovers some latent magic powers on his own before getting his Hogwarts letter. He might face more difficulties and prejudices from the muggles around him, which could make his entry into the wizarding world even more of a relief.
Sirius could help Harry cope by sharing his own experiences of being an outcast in his family. He could tell Harry that just because his parents did this horrible thing, it doesn't mean he's unlovable. Sirius could also introduce Harry to his friends in the wizarding world, like Remus, who could also offer support and friendship.
A plotline could involve them discovering new magical abilities or powers as a result of this trauma. It's possible that the emotional upheaval of being disowned unlocks latent magic within them. They could then use these new powers to not only better their own situation but also to help other outcasts in the wizarding world. Maybe they start a secret group for those who have been rejected by their families.
One interesting plotline could be Fem Harry learning magic in a more unorthodox way under Sirius's guidance. Since Sirius is a bit of a rebel, he might teach her some spells that are not typically part of the Hogwarts curriculum early on. Another plotline could involve Fem Harry dealing with the challenges of being a female in the wizarding world, which has its own set of expectations and biases, all while having Sirius as her main support system. And perhaps there could be a plot where they go on secret adventures together, exploring parts of the wizarding world that are off - limits or forgotten.
One possible plotline could be that Harry discovers a powerful time - traveling spell in his third year at Hogwarts. He decides to use it to go back in time and save his parents. Along the way, he has to face challenges like avoiding detection by the time - turner regulations and dealing with dark wizards who are also lurking in the past.
One possible plotline could be Naruto growing up feeling extremely lonely and trying to find ways to gain his parents' attention even though they're not around. He might start to excel in ninja training not just to prove himself to the village but also in the hope that his parents would be proud if they were there. Another could be Naruto having vivid dreams about his parents and then waking up to the harsh reality of their absence, which could fuel his determination to find out more about them and why they ignored him.
A possible plot is that Harry, after being left by his parents, is raised by a wizard who lives in seclusion. This wizard has a very different view of magic compared to the mainstream wizarding world. Harry learns from him and as he gets older, he decides to go out into the world to seek revenge on those who he believes are responsible for his parents leaving him. Along the way, he meets new friends and foes and has to make some tough decisions about his path in life.
One plotline could be Harry finding a new family among his friends at Hogwarts. They become his support system and help him grow in ways his biological parents couldn't. Another could be Harry's journey to discover why his parents disowned him and uncovering some dark family secret along the way.
One interesting plotline could be Sirius teaching Harry advanced magic in secret. For example, Sirius might show Harry how to perform Patronus charms earlier than he does in the original story. This would give Harry an edge in dealing with Dementors and other dark creatures.