Perhaps the founders return due to a powerful spell gone wrong that breaks the time - space continuum. When they come back, they are shocked at how Hogwarts has changed. They might then set out to find the essence of Hogwarts that they originally created. They could interact with the current students, with Gryffindor inspiring courage, Ravenclaw stimulating intellectual curiosity, Hufflepuff promoting loyalty and Slytherin guiding ambition in a more positive light.
One possible plot could be that the founders return during a time of great crisis at Hogwarts. Maybe a new dark force is emerging and their magic and wisdom are needed to combat it. They could help modernize some of the old Hogwarts traditions while also teaching the students the purest form of magic that was once known in their era.
Well, it could be about the founders coming back to Hogwarts to fix some long - standing issues. Maybe they return to deal with the dark magic that has seeped into the school over the centuries.
Well, it could be about Harry discovering he has a special connection to the four founders. Maybe he finds ancient artifacts left by them that give him new powers. He could use these powers to fight Voldemort in a more unique way, uniting the qualities of all four founders in his fight.
Well, it could be about a character named Heram who discovers he is the heir of the founders. Maybe he has special powers that are related to the founders' original intentions for Hogwarts. He might face challenges from those who don't want an heir to emerge, or he could be on a quest to restore Hogwarts to its former glory following the events in the original series.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin would be main characters as they are the ones returning.
It could be Harry Potter himself. Since he has so many special qualities and a deep connection to Hogwarts, he might be revealed as an heir. Maybe he has some latent powers related to one of the founders that haven't been discovered yet.
Obviously, the founders themselves. Salazar Slytherin would be fascinating as he could show a different side of his personality, not just the one associated with the dark wizards who came from his house. Godric Gryffindor would be full of bravado and heroic deeds, inspiring everyone around him.
It could also center around a mystery related to their previous participation in the Triwizard Tournament. Something that was left unfinished or a secret that's now starting to surface. Their return might be triggered by signs or prophecies related to this mystery. They would then have to work together, along with Harry Potter and his friends, to solve it and prevent any potential disasters in the wizarding world.
In this fanfiction, Harry could learn ancient magic directly from the founders. Maybe he'd get special training from Godric Gryffindor in courage - based spells, or study potion - making secrets from Helga Hufflepuff.
Neville Longbottom is another possible heir. He has a strong connection to Gryffindor through his family's long - standing association with the house. His growth from a shy and clumsy boy to a brave and powerful wizard could be part of a story where he is the heir of the founders. His ability to stand up to the Death Eaters in the final battle shows his hidden strength, which could be related to the founders' magic.
Harry Potter himself could be a likely candidate. He has shown many qualities that the founders would have admired, like his courage and loyalty. Also, he has a connection to the Sorting Hat which has knowledge of the founders' intentions. Another possibility could be Hermione. Her intelligence and thirst for knowledge are traits that could be associated with the founders. She could use her knowledge to uncover secrets related to the founders and their heirship.