Well, it depends on what you consider 'good'. Some people might like the ones that focus on Harry's internal struggle while being trained by Grindelwald. For example, there could be fanfictions where Harry has to decide whether to follow Grindelwald's teachings or stick to his own values. However, not all such fanfictions are well - written. Some might have plot holes or out - of - character moments.
Perhaps in the fanfiction, Harry is trained by Grindelwald to face a greater, unknown threat. Grindelwald could be using Harry as a tool to achieve his own ends, but in the process, Harry discovers hidden aspects of the wizarding world. This could include ancient spells or secrets about the origin of magic that Hogwarts has long forgotten or suppressed.
One possible plotline could be Harry initially being forced into the training but then gradually getting intrigued by Grindelwald's knowledge. He might start to question the traditional teachings of Hogwarts. Another could be that Harry is tricked into the training, thinking Grindelwald has good intentions only to discover the truth later.
Well, perhaps in this fanfiction, Grindelwald trains Harry to be a sort of double agent. Harry would learn Grindelwald's ways so that he can infiltrate the dark wizard's followers. Grindelwald thinks he can control Harry, but Harry is secretly using the knowledge to gather information for Dumbledore. Along the way, Harry would face a moral dilemma as he has to pretend to embrace the dark arts while still holding onto his own values.
Harry might start off as a bit naive about the darker aspects of magic. But as he is trained by Grindelwald, he becomes more aware of the grey areas in the wizarding world. His character could become more conflicted as he is exposed to Grindelwald's teachings. He may question his previous beliefs and values.
Harry's character would likely become more conflicted. He'd be exposed to Grindelwald's radical ideas, which might make him question the values he learned at Hogwarts. His sense of right and wrong could be blurred, and he'd have to struggle to hold onto his true self.
In the 'harry trained by grindelwald fanfic', the character development of Harry would be a key point. Harry, who is used to the values of Dumbledore and Hogwarts, now has to adapt to Grindelwald's teachings. This could lead to an internal struggle within Harry. He might question his own sense of right and wrong. Also, the plot could involve Harry using the skills he learned from Grindelwald to face new threats or solve old mysteries in a completely different way than what we expect from the original series. The fic could also introduce new magical elements or interpretations of existing magic based on Grindelwald's knowledge.
Another option is to check some Harry Potter - themed fan communities on social media platforms like Reddit or Tumblr. Sometimes, fans share links to their favorite fanfics in those communities. You might be able to find someone who has read or even written the 'harry trained by grindelwald fanfic' and get a link from them.
Dumbledore would be a great addition. Since he has a long history with Grindelwald, his presence could add a lot of depth and backstory to the fanfiction. Another good character could be Hermione. Her intelligence and knowledge of magic could help Harry in his encounters with Grindelwald. Also, Newt Scamander could be included. Given his experience with magical creatures and his own adventures in the wizarding world, he might be able to offer unique perspectives and assistance.
At first, it might be a relationship based on Grindelwald's self - serving motives. He sees Harry as a tool. But as they spend time together, there could be moments of mutual understanding. Harry might start to see Grindelwald not just as a villain but as someone with complex ideas.