Perhaps an older trainer who has retired from the regular Pokemon battles but is pulled back into action in this new world. They have a wealth of knowledge and experience that they can use to face the new challenges.
It could be a young and inexperienced trainer who is just starting their journey in this new world. They have big dreams but a lot to learn.
A non - trainer character could also be the main character. For example, a scientist who is studying the new world of Pokemon. They might not be interested in battles but are fascinated by the biology and behavior of Pokemon. Their journey could be about making new discoveries and trying to protect the Pokemon world from threats that are not related to battles, like environmental issues.
It could be a scientist who is involved in the study of Pokemon genetics. While trying to understand the mechanics of evolution better, they accidentally stumble upon the new evolution and then become involved in the events that unfold as a result, both in the scientific and the trainer communities.
It could be a Pokemon itself. For example, a Pikachu that has been separated from its original trainer and has to fend for itself in the wild. But then it meets a new friend, either a human or another Pokemon, who helps it start over. This Pikachu could be the focus of the story as it overcomes its past traumas and looks forward to a new life.
Obviously, the main character could be the new Magma Grunt. He could be a fresh recruit with a different perspective compared to the more experienced members of the team.
It could be an ordinary person from our world, like a high school student. They're suddenly thrust into this new world and have to adapt. Their inexperience in this new environment can lead to many humorous and exciting situations.
A young prodigy who has been underestimated all his life. Fed up with being pushed around, he uses his intelligence and unique abilities to rise to power and become the world overlord.
A Charizard might be the main character. Imagine a Charizard that was always too proud and aggressive. Then it turns over a new leaf and becomes more gentle and uses its fire - breathing ability to help others, like warming up cold areas or helping with cooking in a village.
A Ditto could be the main character. Since it can transform into other Pokemon, it could have a unique perspective on different Pokemon species and their lives.
Perhaps a scientist who has been studying Pokemon for years. When Pokemon start to rule the world, this scientist uses their knowledge to figure out how to live in this new situation. They might try to find a way to reverse the situation, or at least make sure that humans are treated fairly under Pokemon rule.
It could be an ordinary person from our world, like a high - school student. They would bring their own set of values and knowledge from the real world into the pokemon world. This contrast between the two worlds could create a lot of interesting storylines.
There's also a possibility that it could be an older character who has been forgotten or underestimated, like Rock Lee. He could have passed on his skills to a new generation but then has to come out of retirement to face a threat that only he can handle in this new dawn of the Naruto world.