A possible storyline is that there is a prophecy about the end of the world which can only be averted if Percy and Apollo work together in a very specific way. They have to find a set of ancient artifacts that are scattered across different realms. Along the journey, they argue and learn more about each other's personalities, but in the end, they manage to fulfill the prophecy and save the world, strengthening their bond as best friends.
Maybe a story where Xion gets into trouble and Roxas has to save her. Roxas discovers new powers within himself during the rescue mission, and Xion realizes how much Roxas truly cares for her. Their bond deepens as they talk about their feelings afterwards.
Well, a possible storyline is Percy dealing with the expectations of the camps of Apollo and Athena. Since he's the son of both in this fanfiction, he might be pressured to be the best in both areas like archery and battle strategy. He could also go on a quest where he has to use his Apollo - given musical talent to charm a dangerous monster and then use Athena - taught wisdom to outwit another foe.
Well, in Percy Jackson fanfiction, a common plot involves Artemis and Apollo being called upon to help Percy in a time of great need. Artemis might come with her hunters to provide backup in a battle, while Apollo could use his powers to heal the wounded. Also, there are storylines where their family drama gets intertwined with the demigod world. Their relationship with Zeus as their father can cause some interesting scenarios. For instance, if Zeus has some new decree that affects the demigods, Artemis and Apollo might have different reactions to it, which then affects Percy and his friends.
Perhaps the plot involves Percy helping Apollo with a secret mission. Since Percy is good at handling tough situations, he could be assisting Apollo in retrieving a lost artifact. They keep their friendship a secret because Apollo doesn't want the other gods to think he's relying too much on a demigod.
There could also be a fanfiction where Percy has to face his inner demons in a more psychological way. Maybe he's haunted by the memories of all the battles he's fought and the friends he's lost. His friends then have to help him through this tough time, and in the process, they learn more about each other's deeper fears and insecurities.
One great Apollo and Percy fanfiction is 'Apollo's Adventure with Percy'. It has an interesting plot where Apollo and Percy team up to face a new threat in the demigod world. The story is full of action and their interactions are really well - written.
Some fanfics have a storyline where Apollo loses his powers and Percy and Annabeth have to help him get them back. This creates a lot of interesting character development as they all learn from each other. Percy's bravery, Annabeth's intelligence, and Apollo's godly knowledge all come into play. There are also emotional moments as they face various challenges along the way, and their friendship or in some cases a more complex relationship evolves.
It could be Hades. He might not like the idea of Percy, a son of Poseidon, being friends with Apollo. Hades could see it as a threat to his own power or plans in the underworld.
One plot idea could be Percy and Annabeth going on a quest that has nothing to do with the main prophecies. They could be exploring an ancient, forgotten land just for the fun of it and to learn more about the world. Along the way, they face challenges that test their friendship like when Percy accidentally angers a local spirit and Annabeth has to use her wits to calm the situation.
Well, it could be about Percy and Apollo becoming friends in an unexpected way. Like, Apollo is in a situation where he loses his godly powers temporarily and Percy helps him out. During this time, they bond over their shared experiences of being different from regular humans. They start to understand each other's strengths and weaknesses, and form a strong friendship.