A character like Harry Potter himself might be initially skeptical of a Highlander. But when he sees the Highlander's combat skills and immortality, he could be intrigued. He might try to learn from the Highlander's fighting techniques to use against Voldemort. On the other hand, a Highlander could be amazed by the magic in the Harry Potter world, like seeing a simple levitation charm.
The witches and wizards from Harry Potter would likely have different reactions to the Immortals from Highlander. The more studious ones, like Hermione, might want to research the origin of their immortality. The Highlander characters, who are used to a more straightforward fight - for - survival world, could be both fascinated and a bit intimidated by the complex magic and politics of the wizarding world. For example, a Highlander might accidentally break some wizarding laws due to his ignorance, and then have to rely on his new wizard friends to get out of trouble.
If a Highlander were to enter Hogwarts, it would be quite chaotic. The students would be curious and a bit scared. Teachers like Dumbledore would be very cautious but also interested in understanding this new being. The Highlander might befriend some students, like Ron, who would be eager to hear tales of his adventures across the centuries. Meanwhile, the Highlander could also offer his combat experience to help train students in self - defense, especially during the times when Hogwarts was under threat from dark forces.