Poseidon might be extremely angry. He could immediately seek revenge on the abuser. After all, Percy is his son and he has the power to protect him.
Poseidon's reaction would be complex. At first, he might be filled with disbelief that anyone would dare to abuse his son. His anger would be a powerful force, not just directed at the abuser but also at himself for not realizing it sooner. He would likely use his influence among the gods and goddesses to make sure justice is served. He would also take Percy under his wing more closely, perhaps teaching him more powerful skills to defend himself in the future and constantly assuring him of his love and protection.
Well, Poseidon could first be in shock. But then, his rage would build up. He might use his godly powers to isolate the abuser in some way, like sending them to a desolate place. He would also likely comfort Percy and vow to never let such a thing happen again. He could also bring Percy to a safe place, perhaps a hidden part of his underwater kingdom where Percy can heal and feel protected.
The abuser might find themselves ostracized by the whole demigod community. Word would spread about what they did, and no one would want to be associated with them. Also, they could be targeted by other protective figures in Percy's life, not just Poseidon. The gods and goddesses who have some connection to Percy or just have a sense of justice would make sure the abuser pays for their actions. They could be cursed to have a series of misfortunes befall them, like always being in the wrong place at the wrong time and facing various dangerous situations.
Often, Poseidon is depicted as heartbroken. He may withdraw from his normal duties and just sit in his underwater palace, watching over Percy's lifeless body or the place where he died. He could also be shown as being very quiet and solemn, his usual boisterous nature gone, replaced by a deep sense of loss.
Percy could initially feel shock and disbelief. He might try to talk to Poseidon to find out why he was betrayed. If that doesn't work, he could become angry and lash out, perhaps even challenging Poseidon directly.
At first, Percy would likely be angry. He has faced so many challenges with the belief that his father was on his side. The betrayal would make him feel like all his efforts were in vain. He could lash out, perhaps even using his powers in a more reckless way. But as time goes on, he might start to question if there's a deeper reason behind Poseidon's actions and try to find out the truth, especially if he still has friends who believe in him and encourage him to look deeper.
Annabeth is often a popular character. She could be in a story where she has to help Percy deal with his relationship with Poseidon. Maybe she gives him advice on how to handle Poseidon's overbearing nature or how to make the best use of the gifts Poseidon gives him.
He might be extremely angry and feel a deep sense of hurt. After all he has done for Poseidon and the gods, being betrayed would shatter his trust. He could go into a period of self - exile, distancing himself from the demigod world and trying to find his own path without the help of his father.
In fanfictions, Poseidon often interacts with baby Percy in a very gentle and protective way. He might use his powers to create a safe environment for Percy, like a special underwater grotto where Percy can be hidden from danger. Sometimes, he sends sea creatures to watch over Percy, like dolphins or friendly sea nymphs.
Poseidon might be presented as a rather powerless god in the context of Percy being abused in fanfic. Despite being Percy's father, he could be constrained by the will of Zeus and other gods, which prevents him from acting decisively to save Percy. Hades, however, might be a more interesting character. He may have his own motives for helping Percy. He could see Percy as a useful tool against the other Olympians or simply as a victim who he can relate to, given his own outcast status among the gods. So, in fanfic, he might play a key role in Percy's journey to overcome the abuse.
In Poseidon and Percy gay fanfiction, the authors usually have a lot of freedom to shape the story. They can play with the characters' personalities and create scenarios where their relationship blossoms in a romantic way. For example, they could write about how Percy discovers new feelings for Poseidon or vice versa. It might also involve elements of Greek mythology being re - interpreted to fit this new relationship concept, like how Poseidon's powers could be used in a more tender or loving way towards Percy.
Annabeth would definitely be involved. As Percy's girlfriend, she is often by his side during his adventures. She could be the one who witnesses Poseidon's pride towards Percy and helps Percy understand the significance of it. Grover, Percy's best friend, is also likely to be there. He might provide some comical relief during the serious moments when Poseidon is showing his pride. Also, other demigods from Camp Half - Blood like Jason, Piper, and Leo could be involved. They could be in awe of Percy's new - found status with Poseidon and might interact with him differently because of it.