They can play the role of the disruptor. Their modern thinking and behavior can disrupt the established order in the fantasy world.
Modern people in fantasy fiction often act as catalysts for change. For instance, they might introduce new forms of combat or communication methods that the fantasy world has never seen before. They could also be the ones to inspire a revolution against an unjust magical regime. They may also play the role of the curious explorer, eager to understand the mysteries of the fantasy world and in the process, uncover secrets that the natives of the world were unaware of.
Modern people can be the ones who bring a fresh perspective. They might question the long - held beliefs and traditions in the fantasy world. They could also be the saviors, using their modern knowledge of science and technology (even if it's just basic knowledge) to solve problems that the magic - based society couldn't. For example, using first - aid knowledge to heal a wounded character when magic has failed. They can also be the ones who get corrupted by the power of the fantasy world and turn into villains, showing how the allure of magic can be too much for a modern mind.