Well, it could be characters like Draco Malfoy. In the original series, he had his moments of growth and in fanfics, he might be one of the main Slytherins to defend Hogwarts. Maybe he finally realizes the importance of the school and his own values change. He could be joined by other Slytherins who were perhaps overlooked in the official story but show their true courage in the fanfic.
She'd probably be a bit of a misfit in Hufflepuff. The values of hard work and loyalty in Hufflepuff might not seem as exciting to her as the action - packed world she's used to. In Gryffindor, she'd fit in better with their courage, but might also clash with some of the more reckless Gryffindors. In Ravenclaw, she could learn a lot from their thirst for knowledge. And in Slytherin, she might understand their ambition, but also be at odds with some of their more underhanded tactics.
Slytherin is also a possibility. He has to be resourceful to make his own web - shooters and manage his double life. In Hogwarts, he might use his cunning to get out of tricky situations, like when dealing with the mysteries and politics within the school. However, his moral compass would likely keep him from the more negative aspects of Slytherin. He would probably be a different kind of Slytherin, one who uses his wits for good.
Maya could be a Slytherin. She's often a bit of a rebel and is very resourceful. Slytherins are known for their cunning and ability to get what they want, and Maya has shown that she can be quite sly when she needs to be in order to protect herself or her friends.
Naruto might also be a good fit for Hufflepuff. He has a strong sense of loyalty and is always there for his friends. He works hard to achieve his goals, which are traits of Hufflepuff house as well. In the Hogwarts environment, he would show that Hufflepuffs can be as powerful as any other house with his ninja skills.
The relationships between the houses can also be inspiring. There's always a bit of rivalry between Gryffindor and Slytherin. You could write a fanfic where students from these two houses have to work together on a project and they learn to see past their differences. And for Ravenclaw, their intelligence can be used to create a story where a Ravenclaw uses their smarts to solve a mystery that has been plaguing Hogwarts for years.
The Gryffindors, of course, are usually very vocal in their support of Harry. They might cheer him on, offer their own magical skills if they can, and be ready to fight alongside him. The Slytherins can have a more complex reaction. Some might side with Voldemort out of fear or ambition, but there could also be Slytherins who see the wrong in Voldemort's ways and secretly support Harry. The Hufflepuffs would likely be focused on protecting the innocent within Hogwarts and providing a sense of stability and comfort during the chaos. And the Ravenclaws might be analyzing the situation, coming up with strategies to help Harry or trying to understand the deeper magic at play in the battle.
I think Percy could be a Gryffindor. He's brave, always ready to face danger whether it's a monster from Greek mythology or a dark wizard at Hogwarts. His courage is one of his defining traits.
You could start with 'Do Gryffindors always have to be brave? And can a Slytherin be as loyal as a Hufflepuff?' This challenges the typical stereotypes of the houses and can form the basis of a really interesting fanfiction where characters break the mold. For example, a Slytherin character who shows extreme loyalty in a situation where it's unexpected.
He could be in Slytherin. His cunning and ability to manipulate situations in the Naruto series could be seen as Slytherin traits. He was always thinking several steps ahead, just like many Slytherins are known for their strategic minds.