Maybe the plot would revolve around the relationship between Percy and the goddess. It could show how they met, fell in love, and decided to have a child. Then it might explore how the other gods and goddesses react to this union and the birth of the child.
The fanfiction could be about the child's journey. As the child grows up, they discover their own identity and powers. They might face enemies who are threatened by their existence, being a product of Percy and a goddess. Percy would then have to protect the child and guide them on their path to self - discovery.
It could be Aphrodite. Given her domain of love, it would be an interesting take. Percy might be charmed by her beauty and grace, and they could end up having a child. The child might inherit Aphrodite's charm and Percy's courage.
In the 'percy marries a goddess fanfiction', perhaps it starts with Percy accidentally stumbling into the goddess's domain. She is initially cold towards him but as they spend time together, she realizes his good heart. Percy, on the other hand, is in awe of her beauty and power. Their relationship develops slowly, facing opposition from other gods and goddesses who think it's not proper. But they overcome all the odds and marry. Their marriage could then be a symbol of a new era of cooperation between mortals and immortals in the fanfiction world.
Well, one possibility could be that Percy has been on some sort of adventure and during that time, he discovers a child in need. He decides to take the child under his wing and brings the child back to his world. Then, he has to deal with the reactions of his friends and family, who are both surprised and a bit worried about this new addition.
Perhaps the story is centered around a mystery that only Percy and the curvy goddess can solve. The goddess might have some special powers that Percy needs to utilize in order to overcome the obstacles. They could also develop an unlikely friendship or even more as they work together.
Well, in a Fem Percy becomes a goddess fanfiction, perhaps the story begins with Percy being in a life - threatening situation. Instead of dying, some ancient magic or a divine intervention transforms her into a goddess. As a goddess, she might have to deal with the politics of the godly realm. For example, there could be gods who don't want a new goddess to disrupt the existing power balance, so they try to undermine her at every turn. And Percy, being Percy, would fight back and try to find her place among the gods.
It could be Aphrodite. Since she is the goddess of love, it would be an interesting twist. Percy might initially resist her charm but eventually be won over by her true self. Their marriage could bring a new understanding of love to the world of the fanfiction.
One possible plot could be that Percy, as a child, has to navigate his newfound smallness while still having the memories of his older self. He might struggle to convince his friends that he is actually Percy, and they initially think it's some sort of trick. Then, he could use his knowledge from his older self to help them in a new and unexpected way, like solving a mystery that the younger versions of them couldn't figure out on their own.
One possibility could be that Percy has been leading a double life. Maybe he had a relationship in the past that he kept hidden, and now the existence of the child is coming to light. The story could explore how he copes with this new reality and how it affects his relationships with his friends and family.
Maybe the child is an orphan with no idea they are a demigod. Percy senses something special about them and decides to adopt them. He then has to deal with the challenges of raising a child while also protecting them from the various threats in the Percy Jackson universe. For example, he'd have to train the child to fight and also keep them hidden from the wrong eyes. He could introduce the child to Camp Half - Blood, where they meet other demigods and start to discover their true identity.
I'm not sure specifically as there could be many different versions of this fanfiction. Generally, it might involve Percy having some special connection to Chaos that sets him apart from his normal demigod status. Maybe he discovers new powers or a new destiny related to the primordial entity of Chaos.