One idea could be Percy using his new powers to travel through different time periods in the demigod world and fix historical disasters. For example, he could go back to the time of the Titan War and prevent certain events that led to great losses. Another plot could involve him exploring different dimensions in space, finding new and strange mythical creatures that exist only in those far - off realms. He might also have to deal with the consequences of messing with time, like creating alternate timelines that start to collide with the original one.
One idea could be Percy discovers a new power related to controlling time and tides that was hidden from him all along. Maybe he can freeze time during a battle to gain an upper hand against his enemies. Another plot could involve Percy traveling through different time periods using his newfound god - like abilities to correct past mistakes in the world of the gods.
One interesting plot idea could be Percy traveling back in time to the era when the gods first came to power. He could witness the creation of the Olympian council and get involved in the early power struggles among the gods. Another idea is that a god sends Percy on a time - travel mission to fix a mistake in the past that is now threatening the present world of demigods. For example, if a powerful magical artifact was lost in the past and its absence is causing chaos in the present.
Well, perhaps in the fanfiction, the Angel of God is a messenger to Percy, warning him of a great catastrophe that will befall the demigod world. Percy then has to gather all the demigods and prepare them for this threat. The angel could also have the power to bestow temporary divine abilities on Percy and his friends, which they use to battle an army of dark creatures. Or it could be that the angel is actually a lost soul from a previous era, and Percy has to solve the mystery of its past to get its help in saving his world.
One idea could be that the Evil God manipulates Percy's friends against him. For example, making Annabeth doubt Percy's loyalty through false visions. Another could be that the Evil God corrupts the demigod world's magic, turning it against the heroes. Maybe the water Percy usually controls starts to harm him instead of help.
Maybe Percy is chosen by the Fates to be their champion in a battle against an ancient evil that threatens to disrupt the very fabric of fate. He has to team up with some unlikely allies, like minor gods who are also concerned about the balance of fate. He would have to learn new skills and face challenges that test his limits.
One idea could be Percy having to face a new and powerful monster that is a combination of multiple mythological creatures. This would test his skills and force him to come up with new battle strategies.
Well, a plot could revolve around Percy accidentally getting this 'God of Sex' title and trying to figure out how to get rid of it. He might go on a quest to find a way to reverse it. Along the way, he meets other characters who either want to use his power for their own gain or help him out of the mess. It could also involve some comical situations where his friends misunderstand his new powers and get into all sorts of awkward situations.
One idea could be Percy having to protect a group of special children who have unique powers related to the Greek gods. Maybe they are descendants of minor gods and are being hunted by some ancient monsters. Another plot could involve Percy teaching these children about their heritage and how to control their powers in a world that doesn't fully understand them.
Perhaps Percy as the God of Justice has to judge the actions of the Olympian gods themselves. This would create a lot of tension as he tries to hold them accountable for their past misdeeds. Or he could be in charge of a special court for demigods who have committed crimes but have valid reasons for their actions, and he has to balance justice and mercy.
Maybe Percy is chosen by the God of Nature (in this fanfiction) to go on a quest to find the missing seeds of the world - trees that once grew so large they held up the sky. Along the way, he meets new mythical creatures related to nature.