Naruto is a must - have main character in this fanfiction setting. Alongside him, there could be a powerful dragon - girl monster. She has the ability to breathe fire and is very strong. Also, a kitsune - like monster girl could be a main character. She is very intelligent and can use illusions, which comes in handy during their quests. These characters would interact with Naruto in different ways, for example, the dragon - girl might start off as a bit of a rival to Naruto in terms of strength but later become an ally, while the kitsune - girl could be more of a strategic partner, helping him plan their moves.
One possible plot could be that Naruto discovers a hidden village of monster girls. He has to learn their ways and help them defend against a common enemy. Maybe there are some dark forces that want to capture the unique powers of the monster girls for their own evil purposes.
Harry Potter himself could be the main character. He has a history of taking on difficult quests and helping those in need. His sense of justice would drive him to help the monster girls on their journey. He could use his skills in Defense Against the Dark Arts and his knowledge of the wizarding world to overcome obstacles.
One potential monster girl could be a centaur - like being. With the lower body of a horse and the upper body of a human - like monster. She would be strong and have great stamina for long travels. And then there could be a phoenix - like monster girl. She could have the power of fire and rebirth. Whenever Naruto is in danger, she can use her fire powers to protect him and then rejuvenate herself if she gets injured.
Maybe a mermaid girl. Since there are water elements in the Harry Potter world as well. She could live in the Black Lake at Hogwarts and help Harry when he has to deal with water - related challenges. Her mermaid magic could be something completely new for Harry to discover.
A group of students from different houses could be the main characters. For example, a Gryffindor boy who is curious about the mystery of monster girls, a Ravenclaw girl who has extensive knowledge about the Forbidden Forest where some monster girls are rumored to live, and a Hufflepuff boy who is always ready to stand up for the underdog, which in this case are the monster girls. They join forces on a quest that changes their view of the wizarding world.
The main character is a male protagonist. And of course, there are various monster girls which can be considered as main characters in their own right as they play significant roles in the story.
Obviously, Naruto would be one of the main characters. And from Monster Musume, characters like Miia could be important. Miia is one of the more prominent characters in Monster Musume, and her relationship with Naruto could be explored. Maybe she could be like a mentor or a friend to him, helping him understand the Monster Musume world better.
Well, a lamia - a half - snake half - human monster girl - would be a great addition. She could use her snake - like abilities to help Naruto in stealth or tracking missions. There might also be a kitsune - a multi - tailed fox - girl. Given Naruto's relation to the nine - tailed fox, there could be an interesting connection between them. And a manticore - girl, with her dangerous yet alluring nature, would also be a potential character.
Obviously, Naruto would be one of the main characters. Since it's a Naruto - centered fanfic, he's likely to be at the core of the story. There might also be his friends like Sasuke and Sakura. They could play important roles in how they deal with Naruto's'monster' transformation or whatever the story has in store for him.
In a crossover with 'Pokemon', characters like Ash and Pikachu could be great inclusions. Ash's experience with different creatures could be put to the test when dealing with the monster girls. Pikachu's electric attacks could also create some interesting interactions with the monster girls' unique abilities.