A fanfic with this scenario could start with Harry arriving at Ouran Highschool on a rainy day. He has his trusty umbrella, which could be a family heirloom or a magical item. As he walks through the school grounds, the students of Ouran Highschool are intrigued by his different appearance and the old - fashioned umbrella.
Well, there could be a love story between Kyoya and a new girl who joins the school. The girl is a bit of an enigma. Kyoya, always the calculating one, tries to figure her out for the sake of the Host Club's business. But as he digs deeper, he discovers her real charm. She challenges his cold - hearted business - like approach to things. They start having little debates and gradually, Kyoya finds himself looking forward to seeing her every day. His feelings grow from mere curiosity to love, and she also starts to see the warm - hearted person beneath Kyoya's calculating exterior.
One possible plot for such a fanfic could be that on a rainy day at Ouran Highschool, a character similar to Harry (maybe with some of his traits) shows up with a special umbrella. The umbrella might have some magical powers related to the rain, like creating a rain - free zone around the holder. And this character could interact with the Host Club members in unique ways because of this umbrella.