One possible main plot could be that Harry and Draco are sent back to the Founders era due to a magical mishap. They might initially be at odds as usual, but then they realize they have to work together to find a way back to their own time. Along the way, they could get involved in the politics and power struggles of the era, and perhaps even have an impact on the relationships between the Founders themselves.
It could be that in the Founders era, there is a prophecy about two boys from the future who will either save or doom the wizarding world. Harry and Draco are those boys. They are faced with the task of proving that they are not a threat to the Founders and their new magical society. They might have to learn the different types of magic used in that era and use it to their advantage while also dealing with the prejudices of the time, as they come from a future with different social structures.
The main plot might revolve around a mystery in the Founders era that has some connection to Harry and Draco's present. For example, a dark magic that was sealed away in the past is starting to resurface in their time, and they are sent back to stop it from ever being created. In the Founders era, they could meet the young versions of the people they know from history books and have to convince them to take certain actions.
Harry might become more aware of the roots of magic and the origin of the wizarding world's values. His sense of justice could be challenged as he sees the different ways the Founders dealt with problems. Draco, on the other hand, could start to see the value in things other than pure - blood status. He might be exposed to the fact that the Founders had different ideas about what made a great wizard, and this could make him re - evaluate his own beliefs.
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.
One common theme is the exploration of Hogwarts' history. Since the founders are involved, these fanfics often dig into the secrets and legacies of the school. Another theme is the growth and change of the characters. For example, Draco might move away from his pure - blood supremacist views. And of course, friendship (or the building of it) among Harry, Hermione, Neville, and Draco is also a big theme as they have to work together in many of these stories.
Another plot could be the internal conflict within the Badger Clan founders. There could be different ideas about how the clan should be run, what values should be emphasized. Some might want to focus on combat and military strength, while others on diplomacy and trade. This conflict could shape the future of the clan as they try to resolve it during the founders era.
One possible plot twist could be that they go into Slytherin and are initially shunned by the other Slytherins. But then they discover a hidden group within Slytherin that has different values from the traditional Slytherin ones. This group is more inclusive and values knowledge and friendship over pure - blood supremacy. Harry and Hermione then work with this group to change the perception of Slytherin within Hogwarts.
One possible plot twist could be that the founders' different teaching styles clash when raising Harry. For example, Salazar Slytherin might be more strict about pure - blood heritage, while Helga Hufflepuff would focus on his kindness. This could lead to internal conflicts within Harry as he tries to balance their different expectations.
Well, perhaps it could be a fanfic where they are on a secret mission together. After getting dirty during the mission, they find a single shower area in an old, abandoned building. They have to take turns, but there are some magical artifacts in the shower that start causing strange things to happen. Harry might be the first to notice something odd, Hermione would try to analyze it, and Draco would be reluctantly involved.
The plot could involve Harry and Draco being accidentally transported to Burdel during Redada. They have to find a way to get back to their own world while also dealing with the chaos in Burdel. For instance, they might encounter strange creatures or dark wizards that are taking advantage of the Redada situation.
One idea could be exploring the relationships between the four founders before Hogwarts was fully established. For example, how did they meet and decide to build a school together? Another could be delving into the creation of the sorting hat and the initial sorting criteria. Maybe there was a big debate among the founders about it.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin would be main characters as they are the ones returning.