Well, a cool plot might be that the phoenix is actually a reincarnation of an ancient Greek hero. Percy has to figure out who it was in its past life and how it ties into the current threats they face. The phoenix could also have the ability to travel through different realms, and it takes Percy on a journey to places he's never been before, like hidden parts of the Underworld or forgotten islands full of mythical creatures.
One idea could be that the Phoenix King has a connection to an ancient prophecy in the Percy Jackson world. Maybe he is the key to saving Camp Half - Blood from a new, powerful enemy. For example, his powers of rebirth could be used to revive a fallen god who is crucial in the fight against the enemy.
One idea could be Percy getting involved with the Order of the Phoenix somehow. Maybe he's sent on a mission by the gods to help them out. He could use his water powers in new and creative ways within the wizarding world, like using water to put out magical fires or even to disrupt dark magic spells that rely on dryness.
Well, a cool plot could be that the Order of the Phoenix mistakes Percy for a dark wizard at first because of his ability to control water in strange ways. As they try to capture him, Percy has to prove his good intentions. Meanwhile, some of the demigod enemies see this as an opportunity to attack while Percy is distracted. And then, of course, there could be a prophecy that ties the demigods and the wizards together in this strange situation.
One idea could be Percy joining the Order of the Phoenix. He could bring his unique demigod powers to the fight against Voldemort. His ability to control water might be useful in various magical battles, like putting out dark magic - induced fires or creating water barriers.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be Percy and his friends getting trapped in a virtual game world that's a twisted version of their own. They have to use their demigod skills to defeat the digital monsters and find a way out.
Maybe Percy is sent on a quest to Atlantis because there are rumors of a traitor among the Atlanteans who plans to side with the Titans. Percy has to navigate the complex political situation in Atlantis and figure out who the traitor is before it's too late. He also has to deal with the Atlantean magic which is different from what he's used to.
One idea could be that Percy discovers a hidden realm within the world of the Wanderer. This realm has its own set of rules and challenges that he has to navigate. Maybe he meets new demigods there who have been lost for centuries.
One idea could be Percy having to make a deal with a minor underworld god to save Annabeth from a new and strange curse that's slowly draining her life force. He has to complete a series of tasks in the underworld that test his loyalty and courage more than ever before.
Well, perhaps the shield was once owned by a powerful demigod from the past. In the fanfiction, Percy starts having strange dreams about this demigod and the shield's true origin. As he investigates, he realizes that the shield holds the key to defeating a new, emerging evil that threatens not just Camp Half - Blood, but the entire world of gods and mortals. So, he has to figure out how to unlock the shield's full potential.