Harry would probably be very suspicious and cautious around the Demon King. He has faced so many dark forces that he'd be on high alert. For example, he might try to use his invisibility cloak to spy on the Demon King.
I'm not sure specifically who 'harry potter king of fanfic' is. It could be a fanfiction author who is very well - known in the Harry Potter fanfic community for creating really great stories.
One idea could be that the Demon King somehow infiltrates Hogwarts. Maybe he disguises himself as a new professor. This would lead to a lot of mystery and danger as Harry and his friends try to figure out who he really is.
Power is a common theme. The idea of the Demon King often represents a great and perhaps dangerous source of power. In these fics, characters may be tempted by it or have to learn to control it, like Harry dealing with the new - found power associated with the Demon King concept.
It's a rather strange and untrue statement. 'Harry Potter' is a well - known and beloved fantasy series, not a 'demon fanfic'. Fanfic usually refers to fan - created fiction, but this description completely misrepresents the essence of the Harry Potter world which is about magic, friendship, and the battle between good and evil in a fictional magical universe.
In this fanfiction, Voldemort could also be involved in a different way. Since Harry is now the son of the Demon King, Voldemort might see him as a threat or a potential ally. Dumbledore would surely play a role too. He might be the one to guide Harry or try to keep him from fully embracing his demonic side. And there could be some magical creatures that are associated with the demonic realm, like imps or minor demons that could be characters in their own right.
Well, one possible plot could be that Harry discovers his true heritage as the son of the Demon King gradually. He might struggle with new-found powers that are both a blessing and a curse. He could face opposition from the wizarding world who fear his demonic lineage, while also having to decide whether to embrace or reject his dark side.
One idea could be a fanfic where Harry Potter discovers a hidden portal in Hogwarts that leads him to the time of King Arthur. He could use his magic skills to assist Arthur in battles, perhaps using spells to defeat the enemies that Arthur's knights struggle with. For example, Harry could use the Stunning Spell to incapacitate a large group of invaders.
It could be about Harry Potter being seen as the rightful king in a fan - created story. Maybe it involves a scenario where he has a claim to some sort of throne within the wizarding world, perhaps in an alternate version of the events we know from the original books.
Obviously, Harry Potter is one of the main characters. Since it's about him being a king in some way. Hermione Granger and Ron Weasley are likely to be main characters as well, as they are Harry's closest friends and would play important roles in his new 'king' - like journey. There could also be other characters like Dumbledore, either in spirit or through memories, guiding Harry in his new role.