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.
In the world of Ouran Highschool Host Club, Kyoya noticed something different about Haruhi. He was always so calculated, but around her, his heart seemed to have a mind of its own. Meanwhile, Haruhi was getting tired of the chaos in the Host Club. Kyoya decided to take her away from it all for a while. They went to a quiet library, and as they browsed the books together, Kyoya finally admitted his love for her. Haruhi was surprised but also felt a connection she couldn't deny. And so, their love story began.
Romance is also a big theme. The OC usually gets involved in a romantic relationship with one or more of the host club members. It could be a slow - burn romance or a love - at - first - sight kind of situation.
One common theme is the discovery of new sides of the characters. When a baby is introduced into the story, the hosts who are usually all about entertaining guests in a sophisticated way, now have to show their nurturing and caring sides. Another theme is family - like relationships. The hosts come together to take care of the baby, which is like a little family unit within the club.
The male OC could be an undercover journalist. He joins the host club to expose the so - called 'extravagant lifestyle' of the rich students. As he spends more time in the club, he starts to understand the real personalities behind the hosts and realizes that there's more to them than just their wealthy facades. This could lead to a story full of self - discovery and unexpected friendships.
One idea could be an OC who is a new transfer student at Ouran. She's a bit of a tomboy and accidentally stumbles into the Host Club room while looking for the library. The Host Club members are intrigued by her unique style and she ends up becoming a regular visitor, slowly forming a special bond with Tamaki. She could introduce them to new hobbies like skateboarding.
Romance is often a theme as well. With the Host Club's focus on charming and wooing guests, it's natural that there are romantic elements when combined with the Harry Potter characters. There could be love triangles or unexpected pairings that add a lot of drama and intrigue to the fanfictions.