Some gods might be curious. They would want to study the reincarnated character to understand how this reincarnation process happened. Others could be threatened. If the character has the potential to disrupt the power balance among the gods, they'll try to get rid of them. For example, Zeus might see the reincarnated character as a potential threat to his rule and act accordingly.
One common plot device is the protagonist having knowledge from their past life. For example, they might know about future events in the Percy Jackson world and use that to their advantage. Another is forming unexpected alliances. Since they are reincarnated, they could team up with characters who were previously enemies. Also, there's often the struggle to fit into the existing world while being different because of their reincarnation.
The character can interact through friendship. They might bond with Percy over shared interests or experiences. For example, if they have knowledge of modern pop culture from their past life, they could introduce it to Percy and have a good laugh. Another way is through rivalry. They could compete with Annabeth in terms of knowledge or strategic thinking.
One common plot twist is the discovery of a hidden power. For example, the reincarnated character might suddenly find out they have a unique ability related to a minor god that no one expected. Another is a change in the prophecy. Instead of the original prophecy being fulfilled in the expected way, it takes a different turn because of the reincarnated character's presence. And sometimes, there's a betrayal from an unexpected source, like a character who was thought to be a friend turns out to be working for an enemy due to some dark secret from the past.
One great 'Percy Jackson is Reincarnated' fanfiction is 'Reincarnated Hero'. It has an interesting take on Percy coming back in a different era and having to deal with new challenges while still having his old memories and powers. The author does a wonderful job of portraying Percy's character growth in this new situation.
One popular trope is memory recovery. In many of these fanfics, Percy has to gradually remember his past life as a demigod. It adds an element of mystery and character exploration as he figures out who he was. Another is the 'fish out of water' situation. Since he's reincarnated, he often has to adapt to a new world or time period, which can lead to some really interesting and comical situations.
Make the character have flaws that are relatable. Maybe the reincarnated character is overly confident from their past achievements in their previous life, and this overconfidence often gets them into trouble in the dangerous world of demigods. They have to learn to be more humble and work with others, which is a great character arc.
It would be an amazing experience. You'd have incredible powers, like being able to control the elements or manipulate time. You could interact with all the beloved characters from the Percy Jackson universe in a whole new way. Maybe you'd be a new god, bringing in fresh ideas and changes to the pantheon. And you'd get to see the world of Camp Half - Blood and the other mythical places from a divine perspective.
Yes, in some Percy Jackson fanfics, he could be depicted as a Titan. Fanfic writers often take creative liberties and might come up with unique storylines where Percy has Titan - like qualities or is even reimagined as a Titan for the sake of an interesting plot twist.
A really cool plot twist might be that the reincarnated character realizes they are not just reincarnated into the Percy Jackson world randomly. They are part of a prophecy that was long forgotten. Their actions in this new life will either save or destroy the world of demigods. This would add a layer of high stakes and mystery to the fanfiction.