Another option could be Princess Leia from Star Wars in a crossover fanfic. Although it's a bit of a stretch since it combines three different universes, but it could be really cool. Harry and Leia could bond over their leadership skills and their fight against evil. Harry would be intrigued by her ability to lead a rebellion, and Leia would be interested in the magic of the wizarding world.
There could also be an original princess created just for the fanfiction. She could have unique magical abilities of her own, like the power to control the elements. In this case, she and Harry would have a lot to share in terms of magic, and their relationship could be based on exploring and comparing their different magical powers. This original princess could also come from a completely different type of kingdom, with its own set of magical creatures and lore.
The princess could be a descendant of an ancient wizarding family that once ruled a small kingdom. She might have been hidden away from the wizarding world for her own protection. Harry could discover her existence during his search for something related to the history of magic. Her being a princess would add an element of royalty and mystery to the story, and her connection to the old wizarding family could bring in some interesting plot twists.
It might be a character from a different fairy - tale world that has been magically transported into the Harry Potter universe. Let's say it's Snow White. She retains her beauty and kindness but is now in a world full of wizards and witches. Voldemort or one of his followers wants to use her for some evil purpose and Harry Potter has to save her. He would be quite confused at first but then rises to the occasion.
Percy could be an ordinary young man with a kind heart and a sense of adventure. Maybe he's a peasant who dreams of a different life and ends up meeting the princess by chance.
Well, it could be that Percy, who might be a normal guy in this context, meets the princess in a grand ball. They initially clash due to their different upbringings, but as they get to know each other, they start to fall for each other's unique qualities.
Obviously, the Princess of Hell would be one of the main characters. She would bring her own set of characteristics, motives, and powers to the story. Harry Potter himself would also be a main character as the story is set in his world. He would be the one to either oppose or befriend the princess. Hermione and Ron would likely be involved as well, providing support to Harry and having their own reactions to the new and strange character from hell.
The princess might be from a land that was once at war with the Hidden Leaf. Her marriage to Naruto could be a symbol of peace and unity. She could be a strong ninja in her own right, with skills in stealth and combat, and her personality could be a mix of grace and fierceness.
Well, perhaps Harry Potter, being from the wizarding world, meets a princess from a magical kingdom. He might be initially confused by her different world of royalty but then discovers they share a common goal of protecting their respective realms from dark forces. They could fall in love during their adventures together, with Harry using his magic skills and the princess using her diplomatic and leadership skills to face challenges.
The plot might revolve around the 'Princess of Hell' trying to bring some sort of hellish influence into Hogwarts. For example, she could be on a mission to corrupt the students or steal some powerful magical artifacts from the school for her own dark purposes. However, Harry Potter and his friends discover her plans and try to stop her. They might face many challenges as her powers could be quite different from the usual dark wizards they've faced.
There could also be a model who has some sort of magical connection without actually being a wizard or witch. For example, she might be a descendant of a squib, which gives her a bit of an understanding of the wizarding world already. This would make the relationship between her and Harry even more complex and interesting.
Since I haven't read this particular fanfiction, it's hard to say exactly. But it's likely that the black princess is one of the main characters. There might also be some of the original Harry Potter characters like Harry, Hermione, or Ron who could interact with her.