In this fanfiction, the plot could center around a prophecy that involves the female Percy Jackson and Poseidon directly. She has to prove herself worthy of her father's legacy while also dealing with her own feelings for someone. The 'lemon' aspect could come in when she has some private moments with this person, perhaps on a secluded beach or in an underwater grotto, where they share some sweet and somewhat steamy exchanges.
One plot idea could be that the fem Percy Jackson discovers a hidden underwater realm ruled by Poseidon that no one else knew about. She has to navigate through its mysteries and face challenges specific to that place, all while having a complex relationship with Poseidon that develops into a lemon - themed encounter in a very unexpected way. Maybe there are unique sea creatures there that play a role in their relationship development.
One possible plot could be Percy discovers a hidden underwater grotto dedicated to Poseidon where he finds a magical lemon tree. The lemons have special powers that are only revealed when Percy and Poseidon interact near it. They could then go on an adventure to protect the grotto from a sea monster that wants to destroy it for its own gain.
One idea could be Percy having to face a new threat underwater that only Poseidon can help him understand. Maybe a lost civilization that Poseidon once had a connection with is now causing trouble. Another could be Percy going on a quest to find a powerful artifact that was once Poseidon's but has been stolen, and Poseidon gives him special powers or guidance along the way.
One idea could be Percy feeling betrayed by Poseidon and then finding a new family among other outcasts in the demigod world. He could form a group with them and go on adventures that are not related to Poseidon at all.
One idea could be Percy as a baby having small adventures in the underwater world of Poseidon. Maybe he befriends a baby sea monster. Another could be Poseidon trying to protect baby Percy from the other gods who are suspicious of this half - god baby.
One idea could be her going on a quest to find a lost trident piece that was stolen by a powerful new enemy. This would involve facing various mythical creatures and using her unique powers as Poseidon's daughter.
One idea could be Sally and Poseidon having a secret adventure together that involves solving a mystery related to the sea. Maybe they discover a hidden underwater civilization that is in danger.
One interesting Percy Jackson and female Poseidon fanfiction is 'Poseidon's Daughter'. It has a great plot where the female character, as Poseidon's daughter, embarks on a journey similar to Percy's but with her own unique challenges. The author does a good job of integrating the character into the existing Percy Jackson universe.
A fanfiction could be about a competition among Zeus, Poseidon and Hades, and Percy has to be the judge. The competition could be something like who can best help a small, struggling mortal town without using their full power. This would show a different side of the gods and also test Percy's ability to be fair and objective.
For the female Percy Jackson, you can develop her character by showing her growth in understanding and using her powers. Since she has a connection to Poseidon, she could start off a bit unsure but as the story progresses, become more confident. As for the 'lemon' aspect, if there's a love interest, it can show her vulnerability and a different side of her. For Poseidon, show his fatherly side towards her, his pride or disappointment in her actions which can shape her character development as well.