Maybe Harry discovers that the goblins are being wrongly accused of something in the wizarding world, like being framed for a theft in Gringotts. So he decides to use his influence and skills to defend them, showing that not all goblins are bad and that they have been misjudged.
It could be some of the pure - blood wizard families who have always looked down on goblins and consider them as inferior beings. They might oppose Harry's attempts to defend the goblin because it goes against their traditional views of the wizard - goblin hierarchy.
The goblin might be helping Harry because Harry once did a favor for the goblin's family. In the fanfiction, the goblin could be an expert in ancient magic spells that have been long forgotten. He could teach Harry these spells, which would give Harry an edge in the fight against the forces of evil. For example, a spell that can turn the dark wizard's own magic back on them.
Well, perhaps Harry stumbles upon a goblin in a dangerous situation, like being trapped by dark wizards who want to steal the goblin's magic artifacts. Harry uses his skills and spells to fend off the bad guys and rescue the goblin.
It could be that the Goblin King's magical artifacts are being stolen one by one, and this is weakening his realm. Harry Potter gets wind of this and decides to help. He teams up with some of his Hogwarts friends like Hermione and Ron. They use their combined knowledge of magic and spells to track down the thieves and return the artifacts to the Goblin King, thus saving his kingdom.
Well, perhaps the young goblin is in danger from some dark wizards who want to use its unique magical abilities for evil. Harry Potter, being the hero he is, stumbles upon the situation and uses his skills and magic to fend off the bad guys and save the goblin. Maybe he discovers the goblin has some information crucial to the wizarding world's safety too.
The plot could involve a situation where Harry Potter hires a goblin lawyer to fight against the unfair treatment of house - elves in the wizarding world. He might want to use legal means to change the laws regarding their servitude. Since goblins have their own ideas about fairness and legality, the goblin lawyer could be crucial in formulating a legal strategy for this noble cause.
Maybe the goblin is an outcast in its own community. Harry befriends it, and they discover a conspiracy within the wizarding world and the goblin banks. As they become friends, they use their combined knowledge of magic and goblin lore to expose the conspiracy. Along the way, Harry learns about the complex history and culture of goblins, which changes his perspective on the magical world.
Maybe the goblins are in danger from a new threat in the wizarding world. They decide to build rockets to escape to a different dimension or planet. Harry Potter discovers their plan and decides to help them. Along the way, they face challenges like magical interference with the rocket's engine (caused by other dark wizards) and they have to use their combined magic to overcome these obstacles. This could be a really exciting and action - packed fanfic plot.
Well, maybe the goblin child is in danger because of some dark wizards who want to use the goblin's skills for evil. Harry Potter stumbles upon this situation and decides to protect the child. He could use his magic skills like the Patronus charm to fend off the dark wizards and then find a safe place for the goblin child, perhaps among the friendly goblins in Gringotts.
There could be an entirely new goblin character created just for this fanfiction. This goblin lawyer could be an outcast from the goblin community because of his more progressive views on wizard - goblin relations. Harry, seeing his potential, hires him to help with his legal battles that require a fresh perspective.