One thing to keep in mind when looking for this kind of fanfiction is that the quality can vary greatly. Some might be really well - written with great character development, while others might not be as good. Also, make sure the website you use is reliable and safe. When you do find a story, read the reviews if there are any. They can give you an idea of whether it's worth your time.
One popular 'sirius saves abused harry fanfiction' is 'The Bond of Blood'. In this story, Sirius discovers the extent of Harry's abuse at the Dursleys' and takes immediate action to rescue him. He uses his skills as an Animagus to secretly observe Harry and then stages a daring rescue, whisking Harry away to a safe place where he can heal and grow stronger under Sirius' protection.
Frequently, there's a theme of Hermione's strength in the face of abuse. Even before Sirius saves her, she might be shown as trying to resist or endure. And then after being saved, her growth and how she overcomes the trauma can be a big part of the story. The relationship between Sirius and Hermione can also explore themes of mentorship, where Sirius helps her heal and become stronger.
One great 'Draco saves abused Hermione' fanfic is 'Rescue in the Shadows' where Draco discovers Hermione's situation and risks everything to protect her. It has a really engaging plot and great character development.
In such a fanfiction, Sirius might have to face various challenges while adopting Hermione. For example, there could be opposition from some parts of the wizarding community who might question his motives or his ability to take care of her. However, Sirius, with his strong will and love for Hermione, overcomes these obstacles. He might also help Hermione develop her magic skills further and give her the confidence she lacks due to the abuse she has endured.
One great 'sirius saves harry fanfiction' is 'The Guardian's Promise'. In this fic, Sirius goes to extraordinary lengths to protect Harry from various dark threats at Hogwarts. He uses his skills as an Animagus and his knowledge of the wizarding world's secrets to keep Harry out of harm's way.
One great 'Harry Saves Sirius' fanfiction is 'The Rescue Mission' on FanFiction.net. It has a really intense plot where Harry uses his newly learned advanced magic skills to break into Azkaban and free Sirius. The author does a wonderful job of building up the suspense and the relationship between Harry and Sirius.
One common theme is redemption. Sirius often feels guilty for not being there for Harry earlier, and by saving him from abuse, he is redeeming himself in a way. For example, in many stories, he reflects on how he could have prevented Harry from going to the Dursleys in the first place.
In some versions, Hermione might use her advanced magic knowledge. She could have discovered a spell that counteracts the pull of the veil. Maybe she found a way to disrupt the dark magic associated with it and was able to pull Sirius back from the brink just in time.
Another good one is 'Saving Baby Harry: Sirius's Mission'. In this story, Sirius defies all odds to reach Harry. He battles Death Eaters on his way to the Potter's place. Once he has Harry, he flees to a secret location known only to a few. The fic delves deep into Sirius's emotions during this time, from his fear for Harry's life to his determination to keep the baby safe.
Another one to check out is 'Saving Regulus: Sirius's Mission'. This fanfiction delves deep into the wizarding world's politics and how Sirius has to navigate through it all to reach and save his brother. It has some really interesting characterizations and a great plot line.