There could be a lot of interactions based on their different strengths. Haruhi is very good at handling people and coming up with creative solutions in her own world. Harry is strong in magic and has faced great evils. So when they face a problem together, like an enemy that is using both normal and magical means to cause trouble, Haruhi could use her people skills to gather information and Harry would use his magic to fight. And during their down time, they could just sit and talk about their dreams. Harry might talk about his desire to have a normal life sometimes, and Haruhi might mention her dreams of traveling the world.
Harry and Haruhi would probably start off being a bit cautious around each other. Harry might be confused by Haruhi's non - magical world ways, and Haruhi would be shocked by Harry's magic. But as they get to know each other, they could start sharing their stories. Haruhi would tell Harry about her club and her friends, and Harry would talk about Hogwarts. They might also have some comical moments when Harry tries to use magic in a normal situation and causes chaos.
One possible plot could be that Harry Potter, with his magic skills, accidentally stumbles into the world of Haruhi Fujioka. He notices that Haruhi is in some sort of trouble at school, perhaps with some mean students. Harry uses his magic to play some harmless pranks on those students to teach them a lesson. Then he starts to help Haruhi with her various club activities in a magical way. For example, he could use magic to make the common room of the host club look even more amazing for an event.
They could also start sharing secrets under the table. Snape might reveal some of his past experiences with Harry's mother that Harry never knew. In return, Harry could open up about his own fears and insecurities at Hogwarts. This sharing of personal information could lead to a newfound connection between them, changing their relationship dynamic for the rest of the fanfiction.
There's a Haruhi Fujioka crossover with a magical world. In this fanfiction, Haruhi accidentally stumbles into a magical realm. Her practical nature makes her deal with the magical situations in a unique way. For example, she uses her common sense to solve problems that the magic - users there are baffled by. It's a fresh take on her character.
Crossovers in general are popular because they offer a new perspective. With Haruhi Fujioka crossovers, it's not just about seeing her in a new world, but also about how the themes of the original 'Ouran High School Host Club' can be blended or contrasted with the themes of the other universe. For example, if it's a crossover with a historical setting, the modern - day ideas that Haruhi represents can create a really engaging story dynamic.
One good 'Haruhi Fujioka lemon fanfiction' could be 'A Day with Haruhi' which might explore a different side of Haruhi's character in a unique scenario. However, it can be a bit hard to find really high - quality ones as the genre can be quite niche.
One possible plot is that Harry discovers a hidden prophecy that says only by helping Voldemort can he truly save the wizarding world in the long run. So, he reluctantly starts to assist Voldemort in his conquests, all while secretly planning to turn the tables.
You can try fanfiction.net. It has a large collection of fanfictions from various fandoms, and there's a good chance you'll find some 'Haruhi Fujioka lemon fanfiction' there.
If Dark Naruto were in a Harry Potter fanfic, his interactions with Harry would be intense. Harry, being the hero, would likely see Naruto as a threat. Naruto, on the other hand, might not understand the wizarding world's values and could act aggressively towards Harry. They could end up in a battle where their different powers clash.
One way Marge can help is by being a plot device. Her presence can force the wizard characters to be more cautious about using magic, which adds tension to the story. For instance, if they are in a situation where Marge is nearby, they have to hold back their magical abilities, and this can lead to some interesting and suspenseful scenarios.
One possibility is that they become friends immediately. The elf could be really friendly and show Harry around the elf village or something. Another is that they start off on the wrong foot. Maybe Harry accidentally offends the elf at first, but then they work through it.