Overall, the 'Attack on Titan' manga is highly regarded for its dark and gritty themes, as well as its detailed world-building. The art style is also impressive and adds to the immersive experience.
The old story can give characters a sense of purpose. For instance, if their ancestors had a role in the old story, they might feel compelled to continue that legacy.
The world of Attack on Titan would experience a major transformation with the introduction of Pokemon. Socially, the relationship between people would change as they bond over their Pokemon. There could be Pokemon centers and Pokemarts within the walls. Economically, a new industry would emerge around Pokemon. In terms of combat, as I mentioned before, different types of Pokemon would bring new tactics. Fire - type Pokemon could set the Titans on fire, ice - type Pokemon could freeze them, and so on. Also, the idea of Pokemon evolution could be incorporated into the story. Maybe the more a trainer and their Pokemon fight Titans together, the stronger their bond and the more evolved their Pokemon becomes, making them even more effective against the Titans.
Overall, Attack on Titan's anime adaptation is very close to the manga. Some visual details and pacing might be different, but the core story and key moments are intact. The changes made are often to enhance the viewing experience for the animation format.