Grover would be a bit more cautious. He might be a bit scared of the Norse monsters at first. But as he reads more, he'd start to see the similarities between the Norse and Greek worlds in terms of how nature is involved. He might notice how the Norse also have a connection to the natural world, like the wolves and the trees, and how it compares to his own connection to nature in the PJO universe.
Percy would probably find it hilarious. He has a good sense of humor and would likely enjoy the wild and crazy scenarios fans come up with. He might even share the funnier ones with his friends at Camp Half - Blood.
Some characters might be flattered. Like Percy, he could be happy to see that people are so interested in his story in 'The Son of Neptune' that they write fanfiction about it.
Well, it could be about a BTS member accidentally running into a gymnast YN at a sports event. Maybe they get to know each other gradually and BTS is inspired by YN's dedication in gymnastics. It could also involve YN getting a chance to perform at one of BTS's concerts, creating a unique and exciting plot.
For demigods, it could either reinforce their existing views or introduce new perspectives. If a fanfiction delves deeper into a certain aspect of their world like the powers of a god, they might gain a new understanding. Mortals would have a more comprehensive view of the PJO world. They would learn about different characters and their backstories that might not be fully explored in the original books.
One way is through a charity event. BTS is often involved in charity work, and YN could be performing at a gymnastics - related charity event. They meet there and start interacting. Another way could be if YN is a back - up dancer for another K - pop group and during a big K - pop concert, BTS and YN cross paths.
It can be considered common. There are a large number of PJO fans out there, and fanfiction is a popular medium in fan communities. Since the official books have a set storyline, fanfiction offers a chance to expand on it, so many 'mortals' (fans) are attracted to it.
One great 'athena pjo fanfic' is 'Athena's Wisdom'. It really delves into Athena's character in the Percy Jackson universe. The author does a wonderful job of showing her wisdom and how she interacts with the other characters. It has some really interesting plot twists that keep you hooked from start to finish.