The main characters could include the most powerful counter guardians who are tasked with protecting the universe from the alien menace. There could also be an alien character who has a change of heart and decides to side with the counter guardians, and their journey of self - discovery and integration into the counter guardians' world could be a major part of the story.
Well, one interesting concept could be the unique interpretations of the counter guardians in the context of the alien setting. Maybe they have new powers or abilities to deal with the alien threats.
The main characters would likely include the Ultra Guardians themselves. They are probably a group of trainers with special skills or abilities. There could be a leader among them, who is very experienced and has a deep knowledge of Pokemon.
Since I haven't read it, I can't say for sure. But it could be some popular Pokémon from the Altomare region like Latias or Latios.
Given that it's a Naruto - based fanfic, Naruto Uzumaki might be one of the main characters. He could be the one who discovers the existence of the eternal guardians. Sasuke could also be involved, perhaps in a conflict or alliance with these guardians. And if the fanfic focuses on the shinobi world as a whole, characters like Kakashi or Tsunade might also play important roles. As for the eternal guardians themselves, they could be unique characters with their own personalities and powers.
An old grandfather who lives in the house could be a main character. He has a lot of stories and wisdom. Maybe he has had some previous encounter with aliens when he was young and now he can help the family deal with the situation in the attic. He could be the one to bridge the gap between the humans and the aliens.
Since we don't have much information about this 'guardians novel', the main characters could be people with extraordinary powers who have been chosen or have volunteered to be guardians. They might come from different backgrounds, and their individual stories could contribute to the overall plot as they work together to fulfill their guardian duties.
Obviously, Counter Guardian Emiya is one of the main characters. He will be at the center of the story, driving the plot with his actions and decisions. There could also be characters from the world he is crossing over into. For instance, if it's a crossover with a popular shonen anime world, there might be the protagonist of that world who will interact with Emiya.
Again, without more information, it's hard to say. But it could be the children themselves who are being counted as the main characters, along with the person doing the counting.
In the 'legend of the guardians novel', Soren stands out as a central character. He is on a journey of self - discovery as well as a mission to save his owl kind. Gylfie is his loyal companion, and together they form a great team. Twilight, with his tough exterior and great combat skills, is also a key figure. There are also other owls like Digger, who has his own unique perspective and skills. Each of these main characters plays an important role in the overall story, whether it's in the battles, in the search for knowledge, or in building alliances among the owl tribes.
I don't know for sure, but they could be the fae guardians themselves. Maybe there's a leader among them who is particularly powerful and wise.