One plot idea could be that the exchange student is from a very different magical culture. When she arrives at Hogwarts, Harry is immediately intrigued. They start off as study partners in Defense Against the Dark Arts. As they spend more time together, they discover they both have a shared love for exploring the Forbidden Forest. Their relationship slowly blossoms as they face various challenges in the forest together, like encountering a new and dangerous magical creature.
Perhaps the exchange student is a seer. She has a premonition about Harry and is determined to help him. At first, Harry is skeptical, but as her predictions start coming true, he begins to trust her. They go on a journey to find a way to stop a dark prophecy from coming to pass. Along the way, they develop feelings for each other as they rely on each other's strengths and face numerous obstacles together.
One idea could be that they start to bond over their shared love for a particular magical creature. Maybe they both have a soft spot for Thestrals. As they spend time together taking care of a Thestral calf, their relationship blossoms.
One idea could be a story where a new teacher at Hogwarts has a special connection with a student who is an outcast. The teacher helps the student discover a hidden magical talent. For example, the student might be really bad at the usual spells but is amazing at an ancient form of magic that the teacher is also interested in.
One idea could be that they meet in a magical forest where Lady Artemis is protecting some rare magical creatures. Harry is on a quest related to Hogwarts and they end up having to work together. Their initial distrust turns into admiration as they see each other's skills.
One idea could be that they meet through some magical cross - over event. Maybe a spell gone wrong transports Kitty to the Harry Potter universe. They initially misunderstand each other due to their different worlds' cultures but then gradually fall in love as they discover their shared values like bravery and loyalty.
Well, perhaps Romilda starts off by writing anonymous love letters to Harry. Harry initially ignores them, thinking it's some kind of prank. But as time goes on, he discovers it's Romilda. Romilda then decides to be more upfront and invites Harry to the Yule Ball. At the ball, they share a slow dance and start to see each other in a new light, which kicks off their romance.
Maybe Harry is the only merman in a world where mermaids are common. He faces discrimination at first but then uses his unique abilities to save the underwater kingdom from a great danger. For example, he might have a special power to purify poisoned waters that the mermaids don't have.
One idea could be that Harry Potter is magically transported to the Avengers' universe. He could use his magic to help the Avengers in battles, like creating protective shields with spells. Another idea is that the Avengers are somehow sent to Hogwarts, and they have to learn about magic while also dealing with threats in the wizarding world. For example, Iron Man might try to figure out how to integrate his technology with magic.
Another plot could be set in an alternate universe where Nagini has a different origin. Maybe she was an ordinary snake that was experimented on by dark wizards, and Harry stumbles upon her during his travels. He then decides to help her break free from the dark magic that binds her, and in the process, they form an unlikely bond. This bond could then be tested as they face various threats from both the wizarding world and those who want to use Nagini for their own evil purposes.
Perhaps they form a secret club within Hogwarts where they plan elaborate pranks on the Slytherins. This could involve using their combined knowledge of magic and mischief to outwit their rivals in really creative ways. They might also end up uncovering some dark secrets about the Slytherin common room in the process.
One idea could be a story where Harry discovers a hidden spellbook that once belonged to Lupin's family. With Lupin's help, he tries to decipher the spells inside and in the process, they unearth a long - forgotten mystery about Hogwarts.