In this fanfiction, Naruto's brashness and eagerness to prove himself might be tempered a bit by his relationship with Arceus. He might think more before acting as he doesn't want to disappoint Arceus. Arceus, on the other hand, might become more involved in the affairs of the Naruto world than it would be otherwise, all because of its connection to Naruto.
Arceus, being a god - like being, would probably be very calm and wise. However, in this fanfiction, as it has a relationship with Naruto, it might also show a more affectionate and protective side. It could be a bit aloof at times due to its divine nature, but still show deep care for Naruto.
In this type of fanfiction, a plot point might involve Arceus teaching Naruto some unique skills or abilities that are different from what he already has in the original Naruto story. This could lead to new and exciting adventures for Naruto. Also, the relationship between them, which might be a yaoi relationship in this fanfiction, could bring out different sides of their characters as they interact on a more personal level.
In the Naruto world, it could be Orochimaru. He might be interested in Naruto's newfound Pokémon - related powers and try to capture him to experiment on him. Orochimaru is always after power, and Naruto's unique abilities could be very appealing to him.
Well, it could be that Arceus, being a powerful and god - like Pokémon, sees Naruto's potential and decides to take him under his wing. Maybe Arceus helps Naruto gain new powers related to Pokémon abilities. For example, Naruto could learn to use Pokémon moves in his battles against the Akatsuki or other enemies in the Naruto world.
Harry would likely be very determined and compassionate. He has seen the destruction Voldemort caused, and so he is determined to prevent Tom from going down that path. His compassion comes from his own difficult upbringing and he wants to give Tom a better chance. Tom, on the other hand, would be complex. He may start off with a sense of entitlement and a thirst for knowledge and power, but as he is exposed to Harry's love and different values, he begins to change.
Harry is likely to be his usual self - brave, kind - but also a bit more nurturing as he's adopting Sasuke. He would be patient in dealing with Sasuke's often cold and aloof exterior. Sasuke, on the other hand, would be his brooding self at first. He's full of vengeance in his original story, but in this fanfiction, he might start to let go of some of that as he experiences Harry's care and the new world of magic.
Arceus itself might be a character in a way. Maybe it appears in Naruto's dreams or visions, guiding him on how to use his powers. Also, other characters from the Naruto universe like Sakura, who might be in awe of Naruto's new abilities, and might also play a role in helping him understand and control his powers better.
Minerva would be a strict but loving mother - figure. She would be very protective of Hermione and would use her wisdom to guide Hermione in her magical studies and in life. She might be a bit more relaxed in her personal interactions with Hermione compared to how she is with students at Hogwarts.
The main characters are obviously Naruto and Erza. Naruto is the one doing the adopting. He's a ninja from the Hidden Leaf Village, known for his determination and powerful jutsu. Erza is from a different world, a strong and independent female warrior. She has a lot of combat experience and is very skilled with her weapons and magic.
Well, aside from Naruto and Kurenai, there could be other characters involved too. For example, Naruto's friends like Sasuke and Sakura might play important roles. They could be curious about Naruto's new living situation with Kurenai, and their interactions could add more depth to the story. Also, Kurenai's colleagues in the ninja world might show up, perhaps to offer advice or assistance regarding Naruto's upbringing.
Obviously, the main characters would be Nagato and Naruto. Nagato would be in the role of the adoptive father or mentor, and Naruto would be the one being adopted and mentored.