One idea could be Percy going back in time to the era of the Greek gods' creation. He could witness the birth of the first demigods and learn the true origins of his powers. Another plot could involve him traveling back to a time when a great prophecy was first made and trying to change the course of events to prevent a future disaster.
Well, perhaps Percy goes back in time to when his parents first met. He could then try to influence their relationship in some way. Or he might go back to the time of the Trojan War. There, he could interact with the heroes of that era, like Achilles. He might even find a way to use the knowledge from that time to solve problems in his own time, like dealing with new monsters that have ancient roots.
One idea could be Percy going back in time to the era of the first Olympian gods and having to deal with the raw, unbridled power of those early deities. He might find himself in the middle of a power struggle between Zeus and his father, Kronos, before the Titanomachy. Another plot could involve Percy trying to prevent a major disaster in the past that has far - reaching consequences in his own time. For example, stopping the release of a powerful monster that was supposed to be sealed away long ago.
One interesting plot idea could be Percy going back in time to the era of the Greek heroes. He could meet Hercules and learn from him. Maybe he would have to face the same challenges Hercules did, but with his own modern - day skills and knowledge. Another idea is that he goes back to the time when the gods first emerged and gets involved in the power struggles among them. This could change the entire course of mythology as we know it.
Maybe Percy travels back to the founding of Camp Half - Blood. He could meet the first demigods and see how the camp was established. He could also learn ancient fighting techniques and bring them back to his time to use against modern enemies. This would add a really cool element of anachronism to the story.
One idea could be Percy discovers a new power related to time during a quest. For example, he might be able to freeze time briefly to escape a dangerous enemy. Another could be that he travels back in time to change an event in the past that has a major impact on the present in the world of the Gods.
One idea could be Percy reliving the day he discovers his true identity over and over. Each time he tries different ways to break the news to his mom, like one time being super casual, another time making it a big dramatic reveal. Another plot could be him reliving a battle, and each loop he figures out a different strategy to defeat the monsters more efficiently.
One idea could be Percy having to time - travel back to the very beginning when the primordials first emerged. He could accidentally disrupt the balance of power among them, leading to all kinds of chaos in the present. For example, if he stops a primordial from creating a certain element that is crucial for the modern world's magic. Another plot could involve Percy teaming up with a primordial of time to fix time - loops that are causing disasters in different eras. Maybe he has to enter the time - realm of the primordial, which is a completely different and dangerous place filled with temporal anomalies.
One idea could be that Percy goes back to the time when the gods first came to power. He could try to change the way the gods interact with demigods from the start, leading to a whole new world order for demigods. Maybe he'd teach the early demigods some of the skills he has, like advanced sword fighting techniques.
In a Percy Jackson time travel harem fanfiction, Percy could time - travel to a time when the Titans were still ruling. He befriends some female Titans who are intrigued by his modern - day demigod ways. Along with some female demigods from different points in history that he also meets during his travels, they form an unlikely group. Their main goal could be to stop a future threat that Percy knows about from his own time, but they also have to deal with the complex relationships within the harem.
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.