One reason could be that the goblins have a reputation for unique and powerful magic. Harry might believe that the goblins can offer a different kind of healing that Madam Pomfrey can't. For example, if he has a curse that is of goblin origin, he might think the goblins are more likely to be able to remove it.
Perhaps Harry is in a situation where he can't trust the Hogwarts staff or the Ministry of Magic. He might fear that going to Madam Pomfrey would expose him to unwanted attention or danger. The goblins, on the other hand, operate outside of the normal wizarding establishment and could offer a more discreet form of healing.
The goblin healing magic in this fanfiction could operate on a principle of balance. Since goblins are known for their shrewdness and their understanding of magical contracts and balances, they might heal Harry by restoring the balance within his magic. If Harry has been affected by dark magic, the goblins could use their own brand of magic to counteract it. They might use a series of complex incantations that are specific to goblin magic, which are different from the spells used at Hogwarts. These incantations could be designed to seek out and neutralize the dark magic in Harry's system and then replace it with positive, healing magic.
One important goblin could be Griphook. He's a well - known goblin in the Harry Potter series, and in this fanfiction, he might be the main goblin responsible for Harry's healing. He has knowledge of the secrets of Gringotts and could use that knowledge to aid in the healing process.
In this fanfiction, perhaps the goblins use their unique magic or potions to heal Harry Potter. Maybe they have some ancient healing arts that are not known to wizards. It could involve a complex ritual where they draw on the power of the earth or their own magical heritage to mend Harry's wounds, whether they are physical or emotional.
One possible plot could be that Harry has a very serious injury from a dark magic attack. Madam Pomfrey uses all her skills and some rare potions to heal him. During the process, Harry might have some vivid dreams or memories related to his past and his parents. As he slowly recovers, he also discovers some new magical abilities that seem to be a side - effect of the intense healing process.
Another idea is that there's a student who is allergic to some of the regular ingredients in Madam Pomfrey's remedies. So, she experiments with lemon as an alternative ingredient. This fanfiction could focus on the process of her trying different combinations with lemon to find the perfect substitute potion for that student. It could also show the relationship between Madam Pomfrey and the student as she tries to help them.
One possible fanfic could be about Madam Pomfrey's early days at Hogwarts. Maybe she had to deal with some very difficult magical maladies that no one else knew how to handle. She could have been a young and inexperienced healer then, but her determination and natural talent for healing gradually made her the respected figure she is in the series.
In many fanfictions, goblins are often depicted as highly intelligent. They have a deep understanding of magic, especially when it comes to things like metal - working and ancient spells related to treasure. For example, in some stories, they can create enchanted weapons with powers that wizards can't even fathom.
His Hogwarts experience would be very different. For one, he would have a closer relationship with the hospital wing. He might not get into as many dangerous scrapes as in the original story because he would be more aware of the consequences due to Pomfrey's influence. Also, his reputation could be that of a healer - in - training rather than the 'Boy Who Lived'. His classes might be more centered around potions and herbology as he would have a natural inclination towards those subjects.
Neville could be involved. He could bring some plants from the Hogwarts greenhouse that have healing properties. Luna Lovegood might also make an appearance. She could offer some of her unique and rather strange remedies or just be there to provide her calming and dreamy presence, which could have a positive effect on Harry's mental state during his recovery.
One possible reason could be that he was under the influence of a powerful dark magic or a curse that made him lose control. Another reason might be that he was tricked into believing Hogwarts was a threat to the wizarding world in some extreme way. Maybe a powerful enemy manipulated him to think that destroying Hogwarts was the only way to save everyone.