Well, perhaps Harry gets lost in a magical portal and ends up in Middle - earth near Rohan. He finds Theoden ill or injured. Harry uses his magic, like the spell 'Ferula' to bind wounds or 'Brackium Emendo' to mend broken bones. Then he has to deal with the Rohirrim's suspicion of his strange magic.
I'm not sure which specific story Gandalf is telling as there are many in the Tolkien's works. Maybe it's about the history of Middle - earth, like the battles against the dark forces or the tales of the rings.
It's hard to say. Gandalf has a lot of raw power and experience. He's faced some really tough foes in Middle - earth. But Harry Potter is no slouch either. He's got his own set of powerful spells and the ability to think on his feet. However, I think Gandalf might have the edge. His magic is more of an all - encompassing force, and he's had centuries to master it.
There are quite a few. A lot of these fanfictions explore the idea of how different magical systems interact. In the case of Harry Potter healing Theoden, it might involve Harry having to adapt his magic to the more medieval - like setting of Middle - earth. Some fanfics focus on the emotional and cultural exchange that comes with such an event, not just the physical healing.
Another concept is that Naruto is sent to Middle - earth. There, he could use his ninja skills and chakra powers. He and Gandalf could team up to fight Sauron. Naruto's ability to make friends and inspire others would be really useful in uniting the different races of Middle - earth against the common enemy.
Well, Gandalf is from the Ainur. He was among those Maiar who were sent to Middle - earth. His purpose was mainly to help the good against the forces of evil like Sauron. He was created long before the events in Middle - earth started to unfold. Gandalf's origin story is deeply intertwined with the greater cosmology of Tolkien's world. He had powers that were both magical and related to his wisdom and knowledge, which he used to influence the course of events in Middle - earth.
Gandalf originated from a higher spiritual plane. He was dispatched to Middle-earth with a purpose. His background involves being part of a divine order and having a responsibility to bring hope and resistance against evil.
Naruto would probably be very curious about Gandalf. He'd be asking a million questions about Gandalf's staff, his magic, and his long beard. Gandalf, on the other hand, might be intrigued by Naruto's determination and the strange power of chakra. He could see Naruto as a being with great potential for good in a world full of darkness, just like Frodo in Middle - earth.