A Slytherin girl like Pansy Parkinson could be an interesting love interest. If Harry asks to be resorted, perhaps it's because he's intrigued by Pansy's confidence and the mystery that surrounds Slytherin girls. Their relationship would be full of challenges given the traditional Gryffindor - Slytherin rivalry.
Luna Lovegood from Ravenclaw might be a great choice. Harry might ask to be resorted to Ravenclaw to be closer to Luna. Her unique perspective on life and her dreamy nature could attract Harry in a new way, and being in the same house would give them more time to explore their potential relationship.
One possibility could be that Harry is unhappy with his current social or romantic situation in Hogwarts. Maybe he realizes that the initial sorting into houses has limited his romantic opportunities. So, he asks to be resorted in the hopes of finding a more compatible environment for love. For example, he might be tired of the Gryffindor bravado and wants to be in a house where he can find someone who appreciates his more sensitive side, like in Ravenclaw where there are intelligent and often more introspective students.
If Harry gets resorted into Ravenclaw, Luna Lovegood could be a great love interest. They already have a certain connection in the original series, and in this new scenario where Harry is in her house, their relationship could develop into a romantic one. Luna's unique perspective on life could attract Harry even more.
It could be Ginny. Since Ginny has had a long - standing relationship with Harry in the original series, it would make sense for her to be the main love interest in this fan fiction as well. Maybe Harry is brewing the soulmate potion to reaffirm their connection.
A resort romance fanfic for Harry might be as follows. Harry was at a beautiful tropical resort. One day, while he was lounging by the pool, a girl accidentally splashed water on him. That's how they started talking. They soon found out they were both there to get away from the hustle and bustle of their normal lives. They started doing all kinds of activities together at the resort, like snorkeling in the clear blue waters, taking yoga classes in the open - air pavilion. Their feelings for each other grew deeper with each passing day, and they shared a magical time at the resort.
Obviously, Harry Potter himself is the central character. His journey in Slytherin would be the main focus.
Maybe it could be a fellow shinobi from his own village. They've trained together and over time, feelings develop. This person would understand the shinobi life that Tobirama leads, which could make their relationship easier in some ways, but there would still be 'expenses' like the danger they both face in their missions and how that affects their relationship.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of various fanfics, and there's a good chance you'll find 'Harry resorted fanfic' there.
Well, there's 'Harry resorted fanfic' like 'Resorted Harry and the Hidden Path'. In this story, Harry stumbles upon a secret passage in Hogwarts that leads him to an ancient magic. Also, 'The Resorted Life of Harry' shows how his life changes when he makes a different choice early on at Hogwarts.
One popular 'Harry resorted romance fanfic' could be 'A New Beginning for Harry'. It often explores a different side of Harry's character in a romantic context. Another might be 'Harry's Hidden Romance', which delves into a secret relationship that Harry gets involved in.
It could be Draco Malfoy. In this fan fiction, Draco might have a change of heart towards Harry when he becomes a Slytherin. Their initial rivalry could turn into a deeper connection, with Draco seeing Harry in a new light and falling in love.