A rogue demigod who has been corrupted by dark magic could turn into the Dark Lord. This demigod might have been jealous of Percy's fame and power and sought out dark forces to gain more power. Eventually, they become consumed by this dark power and start causing chaos, with the goal of ruling over both the demigod and mortal worlds.
It could be a powerful, ancient Titan who was banished long ago and has now returned for revenge. Maybe Kronos has an even more evil and powerful form that he takes on, becoming the Dark Lord. He wants to destroy the new order of the gods and demigods that has been established since his last defeat.
One idea could be that the Dark Lord somehow manages to corrupt the powers of the gods. Percy has to find a way to stop this corruption before it spreads across the whole world of demigods. He might have to team up with some unexpected allies, like a group of monsters who also don't want to see the world destroyed in this new, chaotic way.
In Percy Jackson Dark Lord fanfic, the world - building is often an interesting aspect. The dark lord could create their own domain or stronghold, which might be a place full of dark magic and dangerous creatures. This new location would add to the overall Percy Jackson universe. Also, the relationship between the dark lord and the Titans or other ancient powers could be explored. Maybe the dark lord is in league with some of the Titans, or is trying to outwit them to gain ultimate power. And the prophecies in this fanfic could be really different. Instead of the usual prophecies about the demigods' quests, there could be prophecies about the rise and fall of the dark lord, which would drive the plot in new and exciting directions.
Well, Nico di Angelo has a good chance of being a main character in this kind of fanfic. His powers over the dead and his somewhat dark and brooding nature could make him a key figure in the fight against the dark lord. Thalia Grace, with her leadership skills and powerful abilities as a daughter of Zeus, would also be a strong candidate. And then there's Luke Castellan. If the fanfic is set in a different timeline or has some sort of alternate reality, Luke could be brought back in a new role, perhaps as a redeemed character who helps in the battle against the dark lord after having once been on the wrong side.
One possible plotline could be a darker version of their quests. For example, instead of simply fighting monsters to save the world, they might be forced to make morally ambiguous choices. Maybe they have to sacrifice some innocent bystanders to defeat a greater evil. Another could be a power struggle between them where their darker sides come out. Percy could be more power - hungry and Annabeth more calculating in a way that challenges their friendship.
In this type of fanfiction, Percy's godlike nature would make him a force to be reckoned with in the shinobi world. His powers, such as his superhuman strength and his connection to the sea gods, could be translated into shinobi - like skills. For instance, his connection to the sea could allow him to control water - based jutsu more effectively. The 'dark' element might manifest as a darker personality, perhaps caused by some trauma in his past. He could be more ruthless and less likely to follow the traditional shinobi code of honor.
One great 'dark powerful' Percy Jackson fanfiction is 'The Dark Son of Poseidon'. In this fic, Percy discovers a new, darker side of his powers that he has to learn to control. It's really exciting as it shows a more complex and morally ambiguous Percy compared to the original books.
One common theme is the corruption of power. In these fanfictions, the gods or demigods might abuse their powers, leading to a darker and more chaotic world. For example, a demigod could use their abilities for personal gain at the expense of others.
Well, one possibility is a crossover of the two storylines. Percy could meet the Dark Angel characters and they could exchange their skills and knowledge. For instance, Percy could teach them about the Greek gods and in return, they could show him their advanced combat techniques.
He might be shocked and a bit disturbed. Percy is a heroic character, and seeing a 'dark' version of himself in fanfiction would be quite jarring. It's like looking into a distorted mirror of his identity.
He might try to understand the motivation behind it. Maybe he'd think that the author had some issues or was just exploring different ideas. He could approach it from an empathetic angle, but still be firm in his own self - identity and not let it affect him too much.