A really interesting plot could be a time - travel fanfic where Percy and Dionysus end up in ancient Greece together. They have to deal with the different rules and social structures of that time while also trying to find a way back. This would allow for a lot of exploration of the origin of Dionysus' powers and how Percy's modern - day thinking clashes with the ancient ways.
One idea could be Percy having to go on a quest with the children of Dionysus. They could face a new type of monster that is immune to normal weapons but can be defeated by the power of wine, which the children of Dionysus can control. Another could be Percy getting into a friendly rivalry with a son of Dionysus over who can throw the best party at Camp Half - Blood. Maybe they compete to see who can get more demigods to attend their party, and in the process, they learn more about each other's powers.
One idea could be that Dionysus, while in his role at Camp Half - Blood, has a series of dreams about Ariadne. These dreams start to influence his actions and decisions in the camp, making him more introspective. Maybe he starts to introduce new activities related to wine - making (in a safe and age - appropriate way for the demigods) as a way to connect to his past with Ariadne. He could also start to tell stories about her to the campers, which might inspire some of them in unexpected ways.
Some fanfics have the idea of Percy losing his water - controlling powers and having to regain them. But here's the twist: he has to do it by helping a group of water spirits that are being corrupted. It's a really cool plot because it not only focuses on his powers but also on his character growth as he tries to make amends with these spirits.
In some 'Percy Jackson Gifts' fanfics, a unique idea is that Percy's gift is the ability to communicate with long - lost mythical creatures. This allows for new adventures and interactions. Another is when his gift is a time - traveling power which he uses to change certain events in the past to save the future.
A unique plot idea could be that the Greek gods and the wizarding world's magic are actually two sides of the same coin. So, Percy and Harry have to figure out how to use both types of magic to defeat an ancient evil that is trying to destroy both realms. Another one is a plot where the demigods are being hunted in the wizarding world because they are seen as a threat to the balance of magic.
One idea could be Percy having to learn about the unique powers and quirks of being associated with Dionysus. For example, he might have to deal with the power of manipulating plants in a new way, or understand the god's connection to madness in a more personal sense. Maybe he has to use his newfound 'family' connection to Dionysus to solve a mystery in the demigod world that involves some sort of curse related to wine or celebration.
The plot could involve the OC struggling with the reputation that comes with being the son of Dionysus. In the Percy Jackson world, Dionysus is often seen as a bit of a party - god and not always taken seriously. So the OC might have to constantly prove himself to his fellow demigods. He could start out being underestimated but then prove his worth in a quest, like finding a lost magical item that only someone with his connection to Dionysus' powers could locate.
A cool plot could involve Percy as a super soldier being sent on a secret mission by the gods. This mission might be related to a new threat that combines the mortal world's technology and the mythological realm. He would have to use his super soldier skills, like enhanced strength and combat training, along with his demigod powers to succeed.
One unique plot idea could be that Percy discovers he has a special connection to the dragons because of his demigod powers. Maybe he can communicate with them on a deeper level than others. Another idea is that the dragons are the key to solving a new threat to the demigod world, like a powerful ancient evil that only the combined strength of the demigods and the dragons can defeat.
One idea could be Percy having to face a new type of monster that is a combination of all the previous ones he's fought. This super - monster could be created by an ancient and powerful enemy who wants to truly become the king of monsters. Another plot could involve Percy having to enter the realm of the dead to find a weapon that can defeat the king of monsters. Maybe he has to make a deal with Hades to get this weapon.