Another plotline could be that Medusa was once a friend of Percy's family in the past, and when Percy finds out, he feels obligated to save her from the wrath of the gods and the danger she constantly faces as a monster.
Perhaps Medusa has some crucial information that Percy needs to save the world, and in order to get that information, he has to protect her from other threats. So he embarks on a journey to keep her safe.
Perhaps Bianca has been poisoned, and Percy has to find a rare antidote within a time limit. He might have to journey to a far - off land, facing many challenges along the way. Or, it could be that Bianca has been lured into a trap by a false friend, and Percy has to expose the traitor and rescue her from the ensuing danger.
Another way is to check out some Percy Jackson - related fan communities on social media platforms like Reddit. There are often threads where fans share their favorite fanfictions, and you might stumble upon some good 'Percy saves Medusa' ones there.
A possible plotline could be that Tayuya is captured by an evil organization, and Naruto goes on a solo mission to save her. He uses his stealth skills to infiltrate the enemy base.
It could be that a powerful sorcerer in the Avengers' world goes rogue and starts using dark magic. The Avengers don't know how to handle magic, so Harry is called in. He has to face this rogue sorcerer, using his own brand of light magic. Along the way, he might have some clashes with the Avengers' way of doing things, but in the end, they all work together and Harry manages to save the day by defeating the rogue sorcerer and restoring peace in the Avengers' world.
The OC could be a wandering ninja who stumbles upon the situation where Kushina is in danger. Maybe they are initially just passing through, but their sense of justice compels them to step in and save her. Then, they might get involved in the larger Naruto world events as a result of this encounter. They could also form a bond with Kushina, which could lead to different relationships with other characters like Minato or Naruto in the future.
One possible plotline could be that Bernardo gets into a dangerous situation, like being trapped in a burning building, and Tony risks his life to save him. Maybe there's a feud between their groups, but Tony's sense of justice or his personal feelings for Bernardo override that.
Perhaps Artemis gets lost in a strange dimension that is similar to Naruto's world. Naruto discovers her there and has to protect her from the dangerous creatures in that dimension. He uses his skills and knowledge of the area to lead her to safety. Along the way, they might form an unlikely friendship or even more, depending on the nature of the fanfiction.
Another plotline could be that Percy has been wrongly accused of something major, like causing a disaster that he had no part in. Poseidon steps in to prove his son's innocence. He might use his influence among the gods or his ability to see the truth through the ocean's currents to clear Percy's name. This often involves some political intrigue among the gods as well.
In some fanfictions, Naruto could be facing a powerful enemy that he underestimated. Temari steps in and saves him. This event could then trigger a series of events where Naruto starts to study Temari's fighting style to improve his own skills. At the same time, the two of them could get involved in some political intrigue within the ninja villages, as Temari is from Suna and Naruto is from Konoha. Their relationship could be a key factor in the stability between the two villages.
One possible plotline is that Harry is magically transported to the Naruto world and discovers Naruto is in danger from a new, powerful enemy. Harry then uses his magic to fight alongside Naruto and his friends, saving Naruto in the process.