Maybe Harry Potter brings some unique magic or skills he learned in Skyrim back to the wizarding world. He could use Skyrim - style combat magic to fight Voldemort's forces.
Well, it could be that Harry Potter got lost in Skyrim during a magical experiment. After many adventures there, he figures out a way to return. Once back, he has a new perspective on magic. He might introduce new spells or ways of using magic that he discovered in Skyrim, which could change the way magic is taught and practiced in Hogwarts.
Obviously, Harry Potter himself would be the main character. Hermione and Ron might also be involved, as they are Harry's closest friends. They could be amazed or even a bit skeptical about Harry's experiences in Skyrim.
In this fanfiction, Harry Potter as High King could bring Hogwarts - like education to Skyrim. He would establish schools of magic where the Nords and other races could learn spells. He'd also use his knowledge of magical creatures to better handle the ones in Skyrim, like trolls and giants. He might even form an alliance between the wizards of his world and the races of Skyrim to face common enemies.
One possible plot could be that Merlin, having been dormant for centuries, is awakened in the world of Harry Potter. He could then use his ancient magic to help Harry and his friends in their fight against Voldemort. Maybe he teaches them spells long forgotten, giving them an edge in the battle.
Well, perhaps Harry could use his magic skills in the world of Skyrim. He might encounter the various races there like the Nords or the Elves and have to adapt his magic to fit the new environment.
He might use his magic to defeat the dragons in Skyrim. His spells could be a new and powerful force in that world.
Well, the plot could involve Harry using his magic skills in the world of Skyrim. Maybe he's hired to protect a powerful mage in Skyrim from the various threats like dragons or bandits. He'd have to adapt his Hogwarts - learned magic to the different magical rules of Skyrim.
Maybe Harry gets involved in the civil war in Skyrim. He could use his Hogwarts-taught dueling skills to fight in battles, and his knowledge of magic could be used to solve some of the political intrigues. He might also try to find a way to bring peace to Skyrim using his unique perspective on magic.
Well, the story could involve Harry facing different kinds of creatures. In Skyrim, there are dragons, trolls, and various undead. Instead of facing dementors, he'd be fighting draugr. And his wand might be replaced by a magic staff or enchanted weapon found in Skyrim's dungeons.
The plot could involve Harry arriving in Skyrim and being mistaken for a powerful mage. He gets caught up in the political intrigue of the different factions in Skyrim. For instance, the Stormcloaks might try to recruit him because they think his magic can give them an advantage in the civil war. Meanwhile, he's also trying to find a way back to his own world.
The Thalmor could be great antagonists. Their strict control over magic and their anti - human beliefs could put them at odds with Harry. They might see his different form of magic as a threat to their power in Skyrim.