A young and determined trainer named Ash could be a great character to pair with Mewthree. Ash has a lot of experience with different Pokemon and his positive attitude could help Mewthree grow and develop its powers in a positive way.
Another interesting character to pair with Mewthree could be Gary. Gary is a rival of Ash and is very intelligent. He could study Mewthree's powers and abilities, and together they could explore new ways to use Mewthree's unique skills. Gary's competitive nature could also push Mewthree to become even stronger.
Misty could also be a good pairing. She is strong - willed and has a deep understanding of water - type Pokemon. Her skills and knowledge could complement Mewthree's abilities, especially if Mewthree has some water - related powers in the fanfiction. Together, they could face many challenges and form a great team.
In some fanfictions, Mewthree could be the result of a genetic accident involving Mew and another powerful Pokemon. It has a split personality - one side is gentle and wants to live in harmony with other Pokemon, while the other side is aggressive and wants to prove its superiority. A group of trainers must figure out how to bring out the good side of Mewthree and control its power.
Blue could also be an interesting character to pair with Leaf. Their different personalities would create a lot of interesting dynamics. Blue's cocky attitude could contrast with Leaf's more calm and collected nature, leading to some fun interactions and perhaps even some friendly rivalries.
Lillie is an obvious choice. In the original Pokemon story, she has a strong connection with Nebby. Their relationship can be further explored in fanfiction, like Lillie teaching Nebby new skills or Nebby protecting Lillie from danger.
I think Professor Sycamore would be an interesting character to pair with Calem in fanfiction. Calem could be his assistant for a special research project on Mega Evolution. This would give Calem a chance to learn more about the secrets of Pokemon from the professor. Also, Tierno could be paired with Calem. They could have a dance - off with their Pokemon, which would be a really fun and unique scenario in the fanfiction.
The protagonist from Pokemon Ruby would be a great character to pair with Courtney. They could have different goals at first but then find common ground in protecting the Pokemon world. Another good character to pair with her could be a wise old Pokemon trainer who has a lot of knowledge about the Ruby region and can offer her valuable advice. Also, a young and enthusiastic Pokemon ranger could be paired with Courtney. Their different personalities could create interesting interactions as they work together on various Pokemon - related tasks.
Professor Oak could also be a good pairing. Gary could learn more about Pokemon research from his grandfather, and they could have adventures together in search of new Pokemon species or to study Pokemon behavior.
In these stories, a good character to pair with Ash is May. May's adventurous spirit can match well with Ash's hybrid - enhanced adventures. She can be excited about exploring new places and Pokemon that Ash's hybrid nature might lead them to. Another one is Clemont. His scientific knowledge can be very useful in understanding Ash's hybrid physiology. He could be constantly trying to figure out how Ash's hybrid abilities work and come up with new strategies for battles. And Lyra from the Johto region can also be a great pairing. Her gentle nature can balance out any wild sides of Ash's hybrid self.
Ash is a great choice. He has a lot of experience with Pokemon and his kind heart could make for an interesting dynamic with Latios. He might be able to understand Latios' needs and help it in its journey. Another good one is Misty. Her strong - willed nature could contrast with Latios' more mysterious side, and they could learn from each other.
Ash and his Pikachu would be great to pair them with. There's always been that rivalry between Team Rocket and Ash, and it could lead to some really fun and exciting interactions. Maybe in this fanfiction, they end up having to team up against a greater threat.
Serena could be paired with them. She has her own dreams and skills in the Pokemon world. Her relationship with Ash could bring in some interesting romantic sub - plots. And then there's Eevee. Eevee is a very adaptable Pokemon. It could befriend Bonnie easily and help them in their adventures, like using its different evolution forms to solve various problems.