One idea could be Percy discovers a new power within him that is related to destruction but he has to learn to control it so as not to harm his friends. Maybe he accidentally causes some chaos in Camp Half - Blood at first.
A third plot idea is that Percy finds out that there is an ancient prophecy about the son of destruction that he is a part of. This prophecy ties in with the fate of the entire demigod world. He has to figure out how to fulfill the prophecy in a way that saves the world rather than destroys it. Along the way, he meets new characters who either help or hinder his journey.
One plot idea could be Percy discovers his new power as the God of Destruction gradually. He might start by accidentally causing small disasters, like making a small pond dry up. As he learns to control it, he could face a great enemy that only his destruction powers can defeat. For example, a powerful titan who is immune to all other forms of attack.
One plot idea could be Percy having to face the Primordial of Destruction in a direct confrontation. Maybe the Primordial is awakened by an ancient evil spell and starts causing chaos in the demigod world. Percy has to gather allies from different camps and figure out a way to stop it before it destroys everything. Another idea is that the Primordial somehow infects Percy with a part of its destructive power, and he has to struggle not to let it take over him while also trying to find a cure. And a third plot could involve the Primordial creating illusions of destruction all over the world, and Percy has to travel through these illusions to find the real source and defeat it.
Well, a great plot idea might be Percy getting involved in a sky - realm war. He has to use his newfound 'Son of the Sky' abilities to lead an army of sky creatures against an evil force. This would involve him making alliances with different beings, like the winged horses or the cloud nymphs. And he'd have to learn how to fly better to be more effective in the battles. Also, his relationships with his friends from Camp Half - Blood would be put to the test as they might not fully understand his new role.
One idea could be Percy discovers a new, forgotten power related to his 'son of love' aspect. Maybe he can heal emotional wounds of other demigods. For example, he helps a demigod who has been traumatized by past battles by using this power.
One idea could be Percy having to prove his divinity in a new way. Maybe he has to face a trial set by the gods where he can't use his usual powers but has to rely on his wits and faith. Another could be Percy interacting with a different pantheon's deities who mistake him for one of their own sons of god. He'd have to navigate their culture and rules.
One idea could be Percy having to face a new water - based monster that is specifically related to the rivers. Maybe it's a shape - shifting creature that can only be defeated by using the unique powers of the rivers. Another plot could involve Percy exploring the origins of his connection to the rivers more deeply and uncovering a long - lost prophecy about a'son of the rivers' that changes his view of his destiny.
One idea could be Percy having to face challenges in a world where Gaea has more direct control over the elements. For example, the earth itself could be constantly shifting and changing, creating new terrains and obstacles for him to overcome. Another could be Percy forming an unlikely alliance with some of Gaea's other children who are also having second thoughts about their mother's destructive plans.
One idea could be Percy having to hide his true parentage from his friends at Camp Half - Blood. He might struggle with the dark powers that come with being Typhon's son while trying to fit in with the demigods who are mostly children of the Olympians. Another plot could involve Percy being hunted by both the Olympians and the monsters because of his unique heritage. The Olympians might see him as a threat, and the monsters might want to use him for their own purposes.
One idea could be Percy discovering new powers related to being the son of Persephone. For example, he might be able to control plant growth in unique ways during battles, like making vines entangle his enemies. Another could be his relationship with the Underworld changing. Since Persephone has a connection to the Underworld, Percy might have a special status there and encounter new mythological creatures or challenges.
One idea could be Percy having to face a new and powerful monster that is immune to water. This would really challenge his typical combat strategies. Another could be Percy getting lost in a forgotten part of the Underworld and having to find his way out while dealing with various underworldly spirits.