There's a 'harry saves sirus fanfic' called 'The Rescue of Sirius'. In this fic, Harry has a premonition of Sirius's danger just in time. He uses his Patronus to send a message to his friends and they all work together to create a diversion while Harry sneaks in to save Sirius.
A great 'harry saves sirus fanfic' might involve Harry teaming up with unexpected allies. Maybe he teams up with some of the Hogwarts ghosts who know secret passages. They help him reach Sirius quickly and he is able to save Sirius from the clutches of Voldemort's minions by using their knowledge of the castle's secrets.
One possible aspect to analyze is Snape's complex character. In many 'Snape Saves Harry' fanfics, it delves deeper into his motives. Snape has always had a love - hate relationship with Harry. In these fanfics, his act of saving Harry might be due to his lingering love for Lily. It shows a different side of Snape, one that is more heroic and self - sacrificing than what we see in the original series at times. This also allows for exploring different plotlines and character development arcs for both Snape and Harry.
I also like 'When Snape Becomes Harry's Guardian'. In this fanfic, Snape saves Harry from a dangerous situation early on, and then takes on a sort of guardianship role. It has some really interesting interactions between the two characters as they learn to live with each other.
A common plotline is that Daphne saves Harry from a dark magic attack. For example, she might notice a cursed object meant for Harry and intervenes just in time.
A plotline could involve Petunia having a change of heart due to a magical event. For instance, she might accidentally stumble upon some of Harry's magic or receive a message from the wizarding world about his importance. This could lead her to stand up against Vernon and protect Harry. She could then start to teach Harry about his mother's side of the family and the magic that runs in his veins in a more positive way than the Dursleys ever did. And perhaps she even helps him develop his magic skills secretly before he goes to Hogwarts.
One common theme is the importance of protecting magical creatures. Harry's act of saving the unicorn emphasizes the value of these wonderful and often endangered beings in the wizarding world.
In a 'Marge Saves Harry' fanfic, the plot could start with Harry ending up in Springfield for some reason. Marge discovers him and his magical abilities. When she learns of the threats he faces in his own world, she decides to accompany him back to the wizarding world. Once there, Marge uses her homemaking skills in a creative way. For instance, she could use her cooking skills to make potions or her knitting skills to create magical items that help Harry in his fight against evil. Along the way, there would be a lot of cultural clashes between the Muggle - like Springfield values and the wizarding world's traditions, which would add an interesting dynamic to the story.
Another theme is heroism. Harry is portrayed as a hero, which is in line with his character throughout the series. But in these fanfics, it's more focused on this one specific heroic act and how it changes things. For example, in some fanfics, it changes the way the wizarding community views Harry, as he's not just the Boy Who Lived but also a savior in a different sense. Also, there's often the theme of defying fate. Cedric was meant to die in the original story, but in these fanfics, Harry's actions change that pre - determined fate, which adds an interesting layer to the story.
Obviously, Harry Potter would be the main character. He is the one doing the saving. Ron Weasley and Hermione Granger are also likely to be main characters as they are Harry's closest friends and often by his side in his adventures. Dumbledore might also play an important role, even if he's dead in the original story, his influence could still be there guiding Harry. And of course, there would probably be villains, perhaps Voldemort or some new dark wizard created for this fanfic.