Hermione would likely be very interested in the Lich King's lore from a research perspective. She could spend hours in the library trying to find out how the magic in that world works. She might even try to adapt some of the Lich King's magic to help in the fight against Voldemort, but with a lot of caution as it's very different and dangerous magic.
The Lich King has a lot of dark and powerful magic. In fanfiction, characters like Dumbledore might be intrigued by it. He could study it to find ways to counter Voldemort. Maybe he tries to understand the nature of the Lich King's control over the undead to see if there are any parallels with Voldemort's control over his Death Eaters.
The Goblin King could interact with Hermione by challenging her intellect. For example, he might present her with a complex riddle related to goblin lore that she has to solve. With Ron, he could have an argument over food or some valuable item that Ron accidentally took from a goblin - owned place. And with Neville, the Goblin King might initially underestimate him but later be impressed by Neville's courage when they face a common threat together.
Azula might be very intrigued by Harry's status as 'the Chosen One'. She could try to use his fame and power to her advantage. Harry, on the other hand, would be cautious of Azula's devious nature. He would likely be hesitant to trust her completely.
Luna Lovegood might have a unique connection with Belphegor. She often has an open - minded view of strange creatures. She could see past his menacing exterior and try to communicate with him on a different level. Harry and his friends might be initially skeptical of her approach but later realize that her way was the key to dealing with Belphegor, either befriending him or getting rid of him.
Android 18 could be a protector for Harry. Given her strength, she could easily fend off Death Eaters. Harry, in turn, could introduce her to the magical world, showing her spells and potions. For example, she might be amazed by the invisibility cloak and they could use it for some strategic advantage.
Hermione could study the Kubikiribocho. She would pour over books in the Hogwarts library to figure out its origin and powers. Harry, on the other hand, might be the one to actually pick it up and test its abilities in combat. Ron could be a bit skeptical at first but would come around when he sees the sword's potential against the dark forces. For example, the sword might react differently to different spells cast at it. Harry could learn to use these reactions to his advantage in battles.
She might interact with Hermione in a way that challenges Hermione's logical view of relationships. Aphrodite could introduce her to a more emotional and instinctive side of love. They could have conversations about how love is not always something that can be explained by books or logic, and this could lead to Hermione having a different perspective on her own feelings for Ron or other potential partners.
They might interact with a mix of awe and curiosity. Harry would be in awe of King Arthur's legend and his noble status. Arthur would be curious about Harry's strange magic. They could start by sharing their stories. Harry would talk about his battles against Voldemort, and Arthur would share his tales of slaying dragons and defending Camelot.
The characters could be initially curious about the staff. For example, Hermione might be eager to study it, to understand its magic which is so different from what she knows. Harry, on the other hand, might be more cautious, sensing the dark power within it.
Perhaps a wizard from Hogwarts gets transported to the world of the Lich King. He has to use his magic in new and unexpected ways to survive among the undead hordes. For example, he could use transfiguration spells to change the appearance of the undead, causing confusion among them.
They could interact in a way where Train Heartnet, being a skilled fighter, could train the students at Hogwarts in combat skills. Harry Potter and his friends might be initially skeptical but then see the value in non - magical fighting techniques. Train, on the other hand, could be amazed by the magic around him and learn a few spells from the wizards.