One great 'Percy Jackson Monster Fanfiction' is 'The Monster's Perspective'. It offers a unique take on how the monsters in the Percy Jackson world view the demigods. It's really interesting to see their side of the story.
There could be a wise old monster who acts as Percy's mentor. Maybe a female monster who becomes Percy's love interest. And of course, there would likely be some villainous monsters who oppose Percy's new existence and try to harm him.
Another theme is the relationship between demigods and monsters. Some fanfictions explore how they can co - exist or even form unlikely alliances. This goes against the typical view in the original series where they are mostly enemies. It shows that there could be more complexity to their interactions, like a monster helping Percy in exchange for something it wants.
Well, obviously Percy is one of the main characters. He's the hero - like figure from the original stories, usually with his own set of powers and a brave personality.
Well, perhaps Percy could start off as a normal person who is suddenly intrigued by the world of monsters. Maybe he gets cursed and starts to transform into a monster himself bit by bit, and has to figure out how to reverse it while also dealing with his newfound monster - like instincts.
One common theme is identity struggle. Percy has to figure out who he is now that he's half - monster. Another theme could be acceptance, both self - acceptance and acceptance from his friends and the wider community in the story. And there's often the theme of power, like how his new half - monster status affects his powers and abilities.
Percy might interact with monsters in a combative way. Since he is often a heroic character, he could be fighting off evil monsters to protect his friends or his world. For example, he could be using his skills to battle a horde of werewolves or vampires.
One interesting aspect could be Percy's character development in relation to the monsters. Maybe he starts off fearing them all, but as the fanfiction progresses, he begins to understand them better. He could learn about their cultures and motives, which would change his perspective. This could lead to him becoming a sort of mediator between the human world and the world of monsters.
I think Cerberus could be an interesting one. It guards the Underworld, and taming it would involve not only dealing with its three heads but also its loyalty to Hades. Percy would have to find a way to convince Cerberus that he's not a threat and that it should follow his commands. It would also open up some cool storylines about exploring the Underworld with a tamed Cerberus by his side.