Maybe Loki adopts Percy because he sees in Percy a power that could be useful for his own plans. But as time goes on, Loki actually starts to care for Percy like a real son. This would change Loki's character development throughout the fanfiction. He might start to make decisions that benefit Percy more than his own self - interested motives, which would be a huge shift for his character.
The plot could also take a turn where Percy's presence in Loki's life reveals secrets about the Norse gods to the Greek demigod world. This could lead to an exchange of knowledge and powers between the two mythologies. However, there could be those in both worlds who oppose this sharing, creating conflicts not just between individuals but also between the two entire mythological systems.
One possible plot twist could be that Percy's demigod powers interact in unexpected ways with Loki's magic. Since Percy has control over water and Loki is known for his trickery, perhaps Loki uses Percy's powers to create illusions involving water, like making a dry desert seem like an ocean to deceive enemies.
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.
At first, their relationship might be rocky. Percy would be cautious of Loki, given Loki's reputation as a trickster. But over time, Loki could use his charm and knowledge to gain Percy's trust. For example, Loki might teach Percy some Norse magic or fighting techniques that Percy didn't know before, which would make Percy see Loki in a new light.
Perhaps in this fanfiction, Loki adopts Peter because he sees potential in him. Peter, being young and inexperienced in some aspects of the wider universe, can be molded by Loki. Loki could use his cunning and knowledge to train Peter not just in combat but also in the art of deception, which could be useful for Peter in his superhero life. They might start by Loki stealing Peter away from his normal life for a short time to show him a different side of existence.
Well, perhaps Loki discovers an orphaned baby in a dangerous situation. He decides to take the baby in out of a sense of pity or a newfound sense of responsibility. Maybe he uses his magic to protect the baby from various threats in the Nine Realms.
Well, a major plot twist could be Naruto being reborn as Percy but still having some of his past life memories. This would lead to him trying to find other reincarnated ninjas in the Percy Jackson universe. Maybe he thinks there are other shinobi reborn as demigods too. Also, his knowledge of seals could be used in a really unique way. He could create seals that interact with the magic in the Percy Jackson world, like sealing away monsters in a way that the demigods have never seen before.
One possible plot twist could be that Percy's wolf - raised nature gives him unique abilities. For example, he might have enhanced senses like super - hearing or smell. This could change the way he approaches battles in the Percy Jackson universe. Instead of relying solely on his demigod powers, he could use his wolf - like instincts to outwit his enemies.
In a 'Percy Jackson adopts Harry Potter' fanfic, the plot could start with Percy being on some kind of mission that crosses into the wizarding world. He stumbles upon Harry, who is alone and vulnerable. Percy decides to adopt Harry because he sees the same kind of determination and courage in Harry that he has. As they journey together, they exchange knowledge. Percy teaches Harry about Greek mythology and combat skills, while Harry shares his knowledge of magic. They form a bond that helps them face threats from both magical and mythological creatures, and they might even team up to fight against a common enemy that is a threat to both their worlds.