Cedric Diggory would be a great main character. He's a well - known Hufflepuff and his values of fairness and hard work would fit well into a story set around a Hufflepuff course.
Obviously, Harry himself is a main character. Then there are often Hufflepuff students like Cedric Diggory. He's a significant character as he represents the best of Hufflepuff - being brave, kind, and fair. Newt Scamander could also be included in some fics as he was a Hufflepuff. His knowledge of magical creatures can add an interesting element to the fanfic.
A plot could revolve around a mystery within the Hufflepuff course. For example, a hidden secret about the founder, Helga Hufflepuff, is embedded in the curriculum. A group of students teams up to unravel this mystery, facing challenges that test their Hufflepuff values like hard work and patience along the way. They could find a long - lost spell or artifact related to the founder.
A Hufflepuff prefect could be the main character. They are responsible for maintaining order within the house and could be caught in the middle of a power struggle between the different houses in this alternate universe. They would have to use their Hufflepuff traits to resolve conflicts and keep the peace in Hogwarts.
Obviously, Harry Potter himself would be the central character. His journey of adjusting to Hufflepuff house would be the main focus.
Perhaps an old Hufflepuff alumni who has turned to the dark side. This person was once a great student but became corrupted over time. They return to Hogwarts with the intention of using the Hufflepuff house as a base for their dark plans. They manipulate the Hufflepuff students, taking advantage of their kindness and hard - working nature, and turn it into a means to an end for their evil deeds. Harry gets caught up in this as he tries to figure out who this mysterious villain is and stop their plans.
In many of these fanfictions, Harry is the central figure, but there are also original Hufflepuff characters created by the authors. These characters might be new students who have some special abilities or knowledge. For example, a young Hufflepuff girl who has an uncanny ability to communicate with magical creatures. Harry teams up with her and other Hufflepuff students to explore a part of the Forbidden Forest that has been sealed off for centuries. Their combined skills of Harry's bravery and the Hufflepuffs' unique talents make for an exciting adventure.
Well, it could be a story where Harry has an encounter with a Hufflepuff student who gives him a glare for some reason. Maybe Harry accidentally stepped on the Hufflepuff's robes during a crowded corridor rush at Hogwarts. And this glare sets off a series of events that leads to an unexpected friendship or a rivalry.
Well, in Harry Potter fanfic, Justin Finch - Fletchley can be an interesting Hufflepuff character. He was a Muggle - born Hufflepuff, and fanfics could tell stories about his initial shock and adjustment to the wizarding world from a Hufflepuff perspective. Pomona Sprout, the Hufflepuff head of house, is also a great character in fanfics. Fanfic authors might write about her teaching methods and how she instilled Hufflepuff values in her students, like her nurturing nature and love for plants which could be tied to the Hufflepuff traits of kindness and patience.
Harry would be the central figure. Ron could be in it too, as he's always interested in food. He could be Harry's taste - tester and also help him source some of the more common wizarding ingredients. And maybe Fleur Delacour could make an appearance, as she has a certain elegance that could be associated with fine dining in the wizarding world.
Another character could be a fellow inmate who has been in jail for a long time. He befriends Harry and teaches him the ropes of surviving in jail.