Maybe the fifth house is a house that was once lost in the history of Hogwarts. In the fanfiction, it could be rediscovered. The plot could involve the characters trying to understand the values and traditions of this ancient house. They might find that the house has a special connection to an old magic that is needed to save Hogwarts from a new threat.
One interesting fifth house Harry Potter fanfiction could be about a group of students who form this new house and they have their own unique set of values and magic. Maybe they are a combination of outcasts from the other houses who come together to create something special.
One idea could be a story where a character from House Reyne discovers a long - lost magic spell that has the power to change the fate of Hogwarts. Another could be a plot where the members of House Reyne form an alliance with other houses to fight against a new dark threat in the wizarding world.
One idea could be a head of house having to deal with a new and dangerous dark magic threat within their own house. Maybe the head of Gryffindor discovers that some students have been dabbling in a forbidden spellbook. Another could be a head of house trying to organize an inter - house tournament to boost morale and unity among the students, but facing opposition from other heads of house who think it's too risky. And a third idea might be a head of house uncovering a long - lost secret about their house's founder that changes the way they view their role and the traditions of the house.
A plot could revolve around a house - elf who gets accidentally mixed up in a dark wizard's plan. Maybe the dark wizard forces the house - elf to steal important magical artifacts from Hogwarts. But the house - elf, having a good heart, tries to find a way to alert the teachers and students without getting caught. Or, there could be a story about a house - elf who befriends a non - magical creature like a Kneazle and they go on an adventure together, exploring the Forbidden Forest and uncovering secrets that are beneficial to the wizarding world.
Well, perhaps in this fanfic, the fifth house could be a house for those with mixed magical abilities. Harry might be sorted into it because he has both Gryffindor - like courage and Slytherin - like cunning. He could then meet new friends who also don't quite fit into the traditional four houses. They would go on adventures together, facing challenges that require the unique combination of traits that the fifth house represents.
A plot might involve Harry Potter as a house - elf being magically bound to serve Draco Malfoy. This would create a really tense situation as Harry has to resist Draco's cruel orders while still trying to figure out how to break the spell. He could also discover that there are secrets in Malfoy Manor that are related to the Dark Arts and the rise of Voldemort. As he tries to expose these secrets, he uses his wits and the skills he has as Harry Potter, even in his house - elf form, to outsmart the Death Eaters and the Malfoys.
One idea could be that Harry grows up with a very different set of values. House elves are known for their loyalty and hard work. So, Harry might be more in tune with serving others selflessly. For example, he could be more eager to help his classmates with their problems without expecting anything in return.
Well, in some fanfictions, a house elf might gain the power to time - travel through some ancient magic. This could lead to them changing the course of events in the wizarding world, like preventing certain dark wizards from rising to power. Also, there could be a story where a house elf uses their magic to communicate with magical creatures that no one else can, and they team up with these creatures to save Hogwarts from a mysterious threat. And then there's the idea of a house elf's magic being misinterpreted as dark magic, and they have to prove their innocence.
Well, perhaps the headmaster realizes that Harry is being influenced by some dark magic remnants in his fifth year. So, he starts a series of magical purification rituals with Harry. This could involve trips to ancient and secret places within Hogwarts and its grounds. Or, the headmaster could be trying to form an alliance of sorts among the students, led by Harry, to be a united front against the rising dark forces. It might also be that the headmaster is trying to uncover the true motives of some of the new teachers who seem a bit suspicious in Harry's fifth year.
A plot could revolve around Ginny getting involved in a secret club or group that Harry is also a part of in their fifth year. This could lead to them having adventures together, exploring hidden parts of Hogwarts. And perhaps they find a mysterious artifact that has some connection to the greater battle against Voldemort. Their relationship could be tested and strengthened through these events.