In a fanfiction where Regulus Black is sorted into Hufflepuff, he might face a lot of prejudice from his own family. They could be disappointed that he's not in Slytherin. But in Hufflepuff, he finds true friends who support him. He could use his intelligence (which is often associated with Slytherins) to help Hufflepuff in things like academic competitions. This would show that being in Hufflepuff doesn't mean he lacks the traits that other houses value.
A fanfiction with this premise might explore how Regulus changes Hufflepuff. His Slytherin upbringing could bring in a different perspective. He might introduce new ways of thinking about magic and the wizarding world to his Hufflepuff housemates. For instance, he could have a more cut - throat approach to Quidditch (a Slytherin trait) which could initially shock the Hufflepuffs but then inspire them to be more competitive in a healthy way. At the same time, Hufflepuff's values start to change him too, making him more open - hearted and less concerned with pure - blood status.
One interesting plotline could be Harry's struggle to fit in with the Hufflepuff values at first. Since he's always been seen as a potential Gryffindor, he has to learn about hard work, loyalty, and fairness in a new way.
Obviously, Harry Potter himself would be the central character. His journey of adjusting to Hufflepuff house would be the main focus.
For creativity. It offers a fresh take on the Harry Potter story. Instead of the typical Gryffindor sorting, Hufflepuff provides a different set of values and dynamics to explore.
One popular one might be 'The Hufflepuff's Adventure'. It often shows Harry's unique journey within Hufflepuff, making new friends and facing challenges in a different way compared to the original story.
Often, Harry will develop a stronger sense of community. Hufflepuff is very much a house that emphasizes togetherness. So he'll start to think more about the group as a whole rather than just himself. He might get involved in house - wide projects to improve the living conditions or organize social events for his housemates.
Another possibility is that Percy is sent to Hogwarts undercover as a Hufflepuff student to investigate some strange magical activity that might be related to the Titans or other Greek monsters. He has to keep his identity as a demigod a secret while trying to fit in with the Hufflepuff house. He could learn a lot from the Hufflepuff way of life, like their patience and kindness, and in turn, he could teach them some things about courage in the face of danger that's different from what they're used to in the wizarding world.
One idea could be exploring Regulus Black's time as a professor and his relationships with students. Maybe he has a student who reminds him of his younger self, and he tries to guide them away from the dark path he once walked. Another could be a mystery where he has to solve a magical riddle in the school that is linked to his past secrets.
One idea could be that Regulus, after faking his death, has been secretly working against Voldemort all this time. He could be gathering intelligence and using his knowledge of the Death Eaters to undermine their plans. Another plot could involve Regulus coming back into the wizarding world and having to deal with the changed perception of him, as everyone thought he was dead. He might also have to face his family again, especially Sirius, and deal with the complex emotions that come with it.
Another plot could be that Regulus, reborn, has memories that are fragmented. As he tries to piece them together, he discovers new secrets about the Black family's past that could change the way the wizarding world views his family. Along the way, he forms unexpected alliances with those who were once his enemies.