There could be many authors. It might be a new writer in the fanfiction community who wants to explore this rather dark and emotional side of their relationship.
Honestly, it could be anyone. There are so many fans out there who write fanfiction. It could be a young fan who was inspired by a particular scene in the original work and decided to write a story where Annabeth makes Percy cry.
There could be many possible authors. It might be an amateur writer who is a big fan of the Percy Jackson series and just wanted to explore this unique scenario. They could be someone within the fan community who is known for writing interesting and out - of - the - box fanfics.
In a fanfiction, it could be that Percy gets influenced by some sort of magic or external force that makes him act coldly towards Annabeth. He starts ignoring her and when she tries to confront him, he says some mean things. Annabeth, who is used to Percy being her support, would be heartbroken and cry.
It could be Chiron, the centaur. He's always keeping an eye on the campers and would likely be concerned if he caught them up to something. He might give them a stern talking - to and some extra chores as punishment.
Maybe Annabeth says something really hurtful about Percy's past, like making fun of his insecurities regarding his father. That could make Percy cry.
One way could be that Percy realizes his mistake right away. He quickly apologizes to Annabeth, explaining that he was just having a bad day or was influenced by something he didn't understand. Annabeth, being in love with him, would probably forgive him after some time.
It could be their friends like Grover. Grover is always around them and he might accidentally stumble upon them while they are in a private moment.
Grover could be one of Percy's friends to meet Annabeth. He's a satyr and has been with Percy through a lot. When he meets Annabeth, he might be really happy to see another important person in Percy's life.
It could be a new demigod who has a grudge against Percy and somehow convinces Annabeth that Percy is a threat, leading to her tying him up. So this new demigod would be the antagonist.
Maybe the main antagonist is an old enemy of Percy's who has learned about his newfound ability to hypnotize (even if it was accidental). This enemy decides to use Annabeth as a pawn by hypnotizing her, hoping to lure Percy into a trap and defeat him once and for all.
It could be a jealous demigod. Maybe someone who has always been envious of Percy and Annabeth's relationship and popularity. This person finds a way to manipulate some dark magic or an old rule to force them into marriage, hoping to create chaos in their lives.