Well, it could start with Percy just happening upon the kid during one of his adventures. The kid might be lost and alone, and Percy's kind heart won't let him leave the kid behind. As Percy adopts the kid, he has to adjust his own life. He might have to find a safe place for them to live, introduce the kid to his friends at Camp Half - Blood, and deal with any potential threats that come their way because of the kid's unknown origin. There could be a lot of heartwarming moments as Percy becomes a sort of father figure to the kid, teaching him life lessons and sharing his own experiences.
Maybe Percy discovers a kid in a difficult situation, like being an orphan in a monster - infested area. He decides to take the kid under his wing to protect him from harm.
In this fanfiction, it could be that the kid has some special power that Percy recognizes. So, Percy adopts the kid to train him and help him control his powers. For example, the kid might be able to control water like Percy but in a wild and uncontrolled way. Percy sees potential in the kid and wants to guide him. He'll teach the kid about the demigod world, how to fight monsters, and how to use his powers for good.
The kid could be a young demigod whose parents are unknown. Maybe he's been living on the streets, hiding from monsters, until Percy finds him.
In this fanfiction, maybe the kid has some special power that Naruto notices. So Naruto adopts the kid to protect him from those who might misuse his power. Along the way, Naruto helps the kid come to terms with his power and they form a really strong bond, facing all kinds of challenges from other villages and ninja clans.
The plot might involve Percy's journey in becoming a father figure. He would have to learn how to take care of a child, which is completely different from his usual adventures. He might face challenges like dealing with the girl's school, her making friends, and also protecting her from any threats that come his way because of his own past or the girl's special circumstances. For example, if she's a demigod too, there could be monsters after her.
In this fanfiction, perhaps Percy adopts Nico after Nico has been ostracized by the other demigods. Percy realizes that Nico needs a safe space. So he offers his home. As time passes, they start to understand each other better. Nico might open up about his past traumas to Percy, and Percy would use his own experiences to help Nico heal and feel like he belongs.
Well, it could be that the kid has some special powers just like Harry. Harry sees himself in the kid and decides to take him under his wing. Maybe the kid is an orphan too, and Harry wants to give him a better life at Hogwarts, away from the cruel muggle world that didn't understand him when he was a kid.
One possible plot could be Percy finding Thalia in a difficult situation, like being hunted by some monsters. He decides to take her in and protect her. He teaches her about the demigod world and they form a strong bond as siblings. They train together to become stronger and face various challenges from the gods and other mythical creatures.
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.
One possibility is that Percy discovers a young demigod girl in a dangerous situation, like being chased by monsters. He decides to take her under his wing and protect her. They then embark on a journey to Camp Half - Blood, facing various challenges along the way.
In this fanfiction, the plot could involve Percy initially being hesitant to adopt Sally's daughter. But as he gets to know her, he realizes she has a lot of potential and a great heart. He starts to provide for her, like getting her into a good school if it's a modern - setting story. And they could go on adventures together, facing challenges that strengthen their bond.
Perhaps the kid is from a foreign land that Naruto visited during one of his missions. The kid could be an outcast in his own place because of some unique trait. Naruto, being the kind - hearted person he is, decides to adopt him. It could be that the kid has a different kind of chakra or a strange mark on his body that makes others afraid of him, but Naruto doesn't care.