There might be a fanfic where a shapeshifter character tries to blend in at Hogwarts while hiding their true form. They could shift into different animals to avoid detection and get involved in various escapades around the school, like sneaking into the Forbidden Forest to find hidden magical artifacts.
One interesting concept could be a shapeshifter who uses their ability to infiltrate the Death Eaters. They could change their appearance to gather intelligence and help the Order of the Phoenix.
Well, there's this fanfic called 'Shapeshifter in the Shadows'. In this story, the shapeshifter character is sort of an enigma at Hogwarts. They use their power to solve mysteries around the castle. Then there's the fanfic where the shapeshifter is actually a descendant of an ancient magical being and has to learn to control their powers in the modern wizarding world of Harry Potter. I can't remember the exact name though. Also, 'Shapeshifting Bonds' is a fanfic that focuses on the relationships a shapeshifter forms because of their unique ability.
There are 'Harry Potter fanfic fanfic' that focus on time - travel scenarios. Imagine if a character from the later books travels back in time to the first year at Hogwarts. This can create a lot of interesting plot twists as they try to change or preserve the original story line. Also, some fanfic fanfic might center around magical creatures in a way that wasn't fully explored in the original books, like the life of a hippogriff in more detail.
A long - lost relative of Sirius Black could be a shapeshifter. Since the Blacks had many secrets and were involved in a lot of dark magic in their family history, it would be believable for a hidden relative to have this unique ability.
Well, I think Orion is a really cool shapeshifter character in some fanfics. He can shapeshift into a powerful dragon, which is just amazing. He uses this form to protect Hogwarts from various threats. There's also a character named Nova. She's a shapeshifter who has the ability to blend into her surroundings by taking on the appearance of the environment. It's a very unique power that she uses in really clever ways. And let's not forget about Thalia, who can shapeshift into different mythical creatures and often uses her powers to help her friends in their adventures.
Some 'Harry Potter and Lily Potter fanfic' might focus on alternate universes. In one such story, Lily could have survived Voldemort's attack. She would then have to raise Harry in a world that is still recovering from the Dark Lord's first rise. This would change a lot of the dynamics in the story. Harry would grow up with his mother's love and protection, and Lily would have to deal with the knowledge that Voldemort could return at any time.
One idea could be a Pokemon that can shapeshift into different legendary Pokemon to gain their powers. For example, it could shift into Mew to use its psychic abilities in unique ways. Another idea is a shapeshifting Pokemon that disguises itself as other common Pokemon to play pranks on trainers. It could be really fun to write about the chaos it causes.
One interesting shapeshifter fiction story is 'An American Werewolf in London'. It tells the story of a man who is bitten by a werewolf and then starts to transform. Another is 'The Wolf Gift' by Anne Rice, which explores the life of a man who becomes a werewolf and his struggle with his new nature. Also, 'The Shape of Water' has elements of shapeshifting as the amphibious creature can change its form in a sense.
I'm not really in favor of the 'slaves' concept in fanfic as it can be a bit disturbing and against the positive spirit of the original 'Harry Potter' series. However, some fanfics might explore power dynamics in a more metaphorical way. But overall, the official 'Harry Potter' works focus on friendship, courage and magic, not slavery themes.
One interesting 'Harry Potter breed fanfic' story could be about the breeding of Hippogriffs in a more domesticated setting. Maybe it explores how wizards are trying to train them for various tasks like mail delivery in a different way than using owls.