Well, it could be simply due to a different kind of chemistry. Sometimes in fanfiction, the author wants to explore an alternative relationship dynamic. Reyna has a certain allure and mystery about her that might attract Percy. And the story could be set up in such a way that Percy and Reyna have more shared experiences at a particular point in time, which makes him lean towards her instead of Annabeth.
One reason could be that Rachel represents a different world to Percy. She's more of an outsider to the demigod world, and Percy might be attracted to that sense of newness and freedom she seems to offer. Maybe he's tired of the constant danger and drama in the demigod life with Annabeth.
Perhaps there are external factors at play. The world of demigods is full of chaos and danger. Reyna might be in a position where Percy feels he has to be by her side to protect her or to fulfill some greater prophecy that involves the two of them, and this leads to him leaving Annabeth.
It would definitely strain Percy's relationship with Annabeth. Annabeth would likely feel betrayed and confused. Their long - standing friendship and the romantic feelings they had for each other would be shattered. As for Percy's relationship with Reyna, it would become more complex. They would have to deal with the fallout from Percy's choice, not just from Annabeth but also from their friends and the overall demigod community.
She could be heartbroken. Annabeth has been through a lot with Percy, and to be rejected for Rachel might make her feel like all their adventures together meant nothing.
One reason could be that Percy is still deeply in love with Annabeth. His loyalty to her is unwavering, so he might reject Reyna out of his commitment to his existing relationship. For example, in the original series, Percy's relationship with Annabeth is built on years of shared adventures and mutual understanding.
One reason could be that Percy has shown great courage and strength, which Reyna respects. She might see in him the potential to be a great ally or even a leader. So, she becomes protective to ensure his safety and to keep him on their side.
One great 'Percy Annabeth Reyna Fanfiction' is 'The Bonds Beyond Prophecy'. It beautifully explores the complex relationships between the three characters. The author does an amazing job of delving into their individual personalities and how they interact with each other in different situations, both in the context of their shared adventures and their personal growth.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
In some fanfictions, Annabeth could abandon Percy because of a prophecy. If the prophecy seems to imply that being with Percy will lead to a great disaster, she might choose to leave to protect him or the world. Also, it could be due to a personal growth arc for Annabeth. She may realize that she has been too dependent on Percy in the past and decides to go off on her own to find her true self, leaving Percy behind.