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.
There could also be new characters introduced in the fanfic. Maybe a young, talented wizard or witch who is just starting at Hogwarts and becomes involved in Harry's return journey. They could bring a fresh perspective and new abilities to the story. And of course, Dumbledore, even if he's not physically present all the time, his influence and legacy are likely to play a role, so he can be considered one of the important characters in a sense.
Fanfics contribute by filling in the gaps. For instance, between the books, there are time periods that J.K. Rowling didn't fully explore. Fanfics can create stories during those times. They also expand on minor characters. Some fanfics focus on characters like Dobby or Kreacher, giving them more backstories and personalities, which in turn adds to the overall richness of the fandom's continuity.
Obviously, the four founders - Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin would be main characters as they are the ones returning.
Perhaps there's a plot twist where the Forbidden Forest reveals a hidden entrance to an ancient magical realm that was previously unknown. This could lead the characters into a whole new adventure, with new magical creatures and challenges that they have to face. It might also hold the key to defeating the remaining threats in the wizarding world.
One of the most popular themes is 'What if' scenarios. For example, what if Harry had been sorted into Slytherin? This allows for a whole new exploration of his character and relationships. Another theme is the post - Hogwarts life of the characters. Fans love to imagine how Harry, Hermione, and Ron navigate the wizarding world as adults. And of course, the exploration of the Marauders' era through the eyes of the new generation is also very popular as it combines the nostalgia of the original series with new storylines.
The plot might revolve around a dark force in the Harry Potter world that has something to do with Horus's inability to return home. For example, a dark wizard could have trapped Horus for some evil purpose. Harry then discovers this and has to battle the dark wizard while also finding a way to free Horus and send him home. There could be epic duels and magical mysteries to solve along the way.
Well, just based on that title alone, it's difficult to determine its quality. There are so many aspects that make a Harry Potter fanfic great. For example, it could explore new relationships between the characters, or create exciting new magical adventures. But we don't know if 'skull is harry potter fanfic' does any of those things. So, it might be good, it might not.
Harry would likely be overjoyed at first. After all, he never really got to know his parents. Their return could give him a sense of family and belonging that he's always craved. It could also help him deal with some of his past traumas, having his parents there to support him.
Horus himself would be a central character. He would bring his own set of powers and a whole different mythology into the story. Dumbledore could also play a significant role. He's wise and powerful, and he might have some knowledge about Horus or the connection between the two worlds. Maybe he's been waiting for Horus to arrive for some greater purpose. And then there could be some minor characters like Neville Longbottom who could end up being unexpectedly helpful in the journey.