Well, Percy has a bit of a rebellious streak. So, he might not just bow down to the gods like most mortals in ancient Greece. He could challenge them on their rules if he thought they were unfair. For example, if the gods had a rule about not sharing certain powers with mortals, and Percy saw that a mortal could use that power for good, he would argue with the gods about it. And if the gods tried to punish him, he would use his own powers and the friends he made in ancient Greece to fight back.
He would probably be cautious at first. Percy knows the power of the gods from his own experiences, but in ancient Greece, they are even more directly in control. He might try to avoid angering them, but if they wronged a mortal unjustly, he would likely speak up. For example, if Zeus was about to strike down an innocent villager, Percy might use his quick thinking to persuade Zeus otherwise.
His birth could introduce new prophecies. For example, the oracles might start predicting things related to Percy's fate that could change the course of events in Greek mythology.
He'd probably be cautious at first. Given his experiences with the Greek gods, he'd know that gods can be unpredictable. He might start by observing the Celtic gods' behavior. Maybe he'd try to find common ground, like their connection to nature or their role in the cosmos.
He could be in awe at first. I mean, they are gods after all. But then he might start challenging them in a friendly way, like he did with some of the Greek gods. He might show off his water - controlling powers to impress them.
The gods also interact with Percy a lot. Zeus might be angry with Percy for interfering in the affairs of the gods in Ancient Greece. Or Poseidon could be guiding Percy secretly, giving him hints on how to deal with the challenges he faces, like when he's on a quest related to the sea.
Athena, being the goddess of wisdom, might analyze the fanfiction. She could look at how the mortal writers understand the Greek mythology and use it to create new stories. She might be impressed by the intelligence and creativity of some of the fanfictions, or she might be critical of inaccuracies.
They might think mortals are more creative. The fanfiction shows that mortals can come up with all sorts of wild ideas about the gods, which could make the gods see mortals as having vivid imaginations.
They might be amused. After all, the fanfiction often portrays them in new and sometimes comical ways. They could find it interesting to see how modern humans imagine their lives and personalities.
He'd probably have a different set of enemies. In Ancient Greece, the threats might be more centered around the local myths and power struggles. For example, he could be in the middle of a feud between two powerful city - states, each with their own godly patrons.
Their relationship could develop deeper as they face more dangerous challenges together. The shared experiences in Ancient Greece would strengthen their bond. For instance, when they are in a life - or - death situation against a powerful enemy, they would learn to trust each other even more.
Percy would probably be initially cautious when interacting with Egyptian gods. For example, when meeting Ra, the sun god, Percy might be in awe but also a bit hesitant as their powers are so different. He would need to show respect as he does with the Greek gods. The Egyptian gods, in turn, might be curious about Percy's abilities, especially his control over water which is not as prominent in Egyptian mythology.