In the fanfiction, Percy becoming a god gives him a new perspective on his relationship with Calypso. He is now able to offer her more than just his mortal love. Their relationship deepens as they plan their wedding. After the marriage, they start to work on projects together, like building a new sanctuary for lost souls. They communicate on a deeper level, understanding each other's desires and fears, and their love continues to grow and evolve in the context of the godly world they now inhabit.
At first, Calypso might be in awe of Percy's new godly form. But soon, they realize that they are equals in many ways. Their relationship develops as they face opposition from some of the other gods. They support each other through difficult times, like when some try to undermine their marriage. Percy, with his courage, and Calypso, with her wisdom, make their relationship strong and they become a power couple in the divine realm.
Their relationship could develop through shared experiences. For example, they might go on a quest together to find a lost relic. During this quest, they learn more about each other's strengths and weaknesses and grow closer.
Percy would likely become more mature. He has already been through a lot, but the relationship with Calypso would force him to think about a more permanent future. He might become more patient as well, as Calypso has her own traumas from being alone for so long. Calypso, on the other hand, would become more open. She has been isolated, but with Percy, she starts to trust more and interact with the outside world again. Her powers might also develop in new ways as she has a new purpose in life - to be with Percy and build a future together.
One possible plot could be that Percy, after becoming a god, has to face the challenges of the divine world. He decides to marry Calypso as they have a deep connection. Their marriage could be a symbol of unity between different parts of the mythological world. Gods and goddesses might be either in favor or against it, leading to various political and personal intrigues within the divine realm.
It can be developed through communication. For example, Percy could write letters to Calypso (even if she's on her island). These letters could express his true feelings for her, and Calypso could respond in some magical way. This exchange of thoughts and emotions would deepen their relationship.
In some fanfictions, their interactions are filled with a bit of tension. Calypso, having been alone for so long, may be hesitant to fully trust Percy at first. But as he continues to visit her and bring her lemons, she slowly warms up. They start to share stories, with Percy telling her about his adventures at Camp Half - Blood and Calypso sharing her knowledge of the island's secrets. Their relationship builds over time, and the lemons can be seen as a symbol of their growing bond.
One possible plot could be that after all his adventures, Percy somehow finds his way back to Calypso's island. They start to reconnect and realize their feelings have deepened over time. Calypso, who has been alone for so long, is hesitant at first but Percy's determination wins her over. They then have to face the challenges of getting the approval of the gods, especially since Percy has a history with some of them. Together, they overcome these obstacles and finally get married in a ceremony attended by their friends from the demigod world and some friendly spirits from Calypso's island.
Often, they start with Percy arriving on Calypso's island. Then, they begin to understand each other. For example, in many fanfics, Percy tells Calypso about his adventures, and she shares her loneliness. This mutual understanding forms the basis of their relationship.
One character that would be really good to include is Circe. She has her own island and magic, and her interaction with Calypso could be fascinating. She might be jealous of Calypso's new relationship or try to use it to her advantage. Poseidon could also be included. As Percy's father, he might have an opinion on Percy's connection with Calypso. And finally, Thalia. She could be the voice of reason for Percy, helping him figure out his feelings and what to do about his relationship with Calypso.
Annabeth would likely be furious at first. She has been through so much with Percy, and for him to leave her for Calypso would seem like a betrayal. But then, she might also start to reflect on their relationship and what went wrong. She could become determined to win Percy back or to move on and prove that she doesn't need him.
In many Percy Jackson fanfictions, Calypso is often portrayed as a complex and tragic figure. She's shown as being both alluring and lonely. Her character is usually depicted with her longing for Percy, as in the original books. Some fanfictions might explore her life on the island before Percy arrived, giving more depth to her isolation.