In the fanfiction, perhaps Voldemort's grandson is not as evil as his grandfather. He could be trying to redeem his family's name. Percy Jackson might initially be suspicious of him but then they team up. The grandson could teach Percy some basic magic, and Percy could teach him how to be brave in the face of real danger, not just the kind wizards face. They might go on an adventure together to retrieve a powerful artifact that could change the fate of both their worlds. This would be a great way to explore the idea of good and evil not being so black and white.
One possible plot could be that Percy Jackson's grandson discovers a portal that leads to the wizarding world. He soon learns about Voldemort's reign of terror and decides to use his demigod powers to stop him. Along the way, he teams up with some young wizards and witches who are also against Voldemort.
One way could be to start with Percy discovering this strange connection. Maybe he has some strange dreams or visions that lead him to investigate. Then he could travel to the wizarding world to learn more about Voldemort. Along the way, he'd face opposition from both demigods who think he's getting too involved with dark magic and wizards who are wary of his demigod status.
Percy would probably rely on his friends. In the Percy Jackson series, his friends were always there for him. In this fanfiction situation, he'd need them more than ever. They could help him stay grounded and remind him of his true self, not the dark legacy of Voldemort. Also, he might learn more about his demigod side to overpower the dark side in him.
It could be a wild mash - up. Percy might inherit some of Voldemort's dark magic tendencies while still having his own demigod powers. Maybe he'd struggle with the dark side of his heritage while trying to be a hero like he is in the Percy Jackson series.
Well, it might start with Percy discovering his strange connection to Voldemort. There could be a lot of confusion and disbelief from Percy's side as he tries to understand how he could be related to such an evil wizard. And in the Harry Potter world, the characters would be equally shocked to find out about this new relation. It would be a story full of mystery and trying to figure out the how and why of this relationship.
Percy might be a bit curious too. He's used to strange things, and meeting someone related to such a powerful dark wizard could pique his interest. He could try to figure out if the grandson has the same evil intentions as Voldemort. He'd likely keep his distance at first, but as he observes the grandson, his reaction could change.
In fanfiction, anything can be possible. However, in the original Percy Jackson and Harry Potter universes, there's no such connection. But in this fanfiction concept, it could mean a very strange blend of magic and demigod powers. Maybe Percy would inherit some of Voldemort's dark magic tendencies along with his own demigod abilities, which could create a whole new set of adventures and challenges for him.
Well, the plot could be centered around Percy's attempts to bridge the gap between his father Poseidon and his grandfather Zeus. There have always been tensions between the two gods. Percy, using his unique position, tries to bring peace. But there are forces at work, like some rogue demigods who don't want peace between the two powerful gods. They try to sabotage Percy's efforts, leading to a series of adventures and challenges for Percy.
One possible plot could be Percy discovering his relation to Dumbledore. Maybe he starts having strange dreams or visions that lead him to the wizarding world. He then has to learn about his new family connection while also trying to keep his demigod identity a secret from most of the wizards, as they might not understand it.
Well, one possible plot could be that Percy discovers his new relation to Hephaestus later in his adventures. He might then start to have an affinity for creating and fixing magical items, which could be a new skill for him in battles against monsters. He could also meet other descendants of Hephaestus who teach him more about his heritage.