Kakashi could also be a mentor figure. He could take a demigod under his wing, like how he mentored Naruto. He would teach them about discipline, self - improvement, and how to face their fears. His ninja training methods could be adapted to the needs of the demigod in the Percy Jackson world, helping them become stronger both physically and mentally.
He might be an antagonist at first. His different set of powers and his somewhat aloof nature could make the demigods view him as a threat. But as the story progresses, they could discover that he's actually on their side and has his own reasons for his actions. For instance, he could be trying to stop a greater evil that the demigods are not aware of yet.
He could be a mentor figure. Goku has a lot of experience in fighting powerful enemies and growing stronger. He could teach the demigods in Percy Jackson's world some new combat techniques.
She often plays the role of a protector. Hestia's connection to the hearth gives her a sense of guardianship. In fanfiction, she might protect the demigods from the more malevolent forces. For example, she could keep them warm during a cold and dangerous night on a quest.
Excalibur could play the role of a unifying force. In fanfiction, it might be the one thing that different groups of demigods or even gods are after. Its presence could create alliances and rivalries. Say, the campers at Camp Half - Blood and the Roman demigods from Camp Jupiter might have to work together or fight over Excalibur. It could also be a symbol of a greater power that is emerging in the Percy Jackson world, leading to new prophecies and quests.
She often plays the role of a love instigator. She can create romantic tension between characters, like making two demigods who initially dislike each other start to have feelings. This adds an interesting dynamic to the fanfiction story.
Naruto could be a mediator. Since he comes from a different world with different power systems, he might be able to bridge the gap between the Shinto gods and the demigods in the Percy Jackson world. He could use his understanding of loyalty and friendship from his own story to help resolve conflicts.
One way could be by making him a mysterious new demigod. He could have his Sharingan ability which might be related to some special power in the Percy Jackson universe, like being able to see through the Mist more clearly than others.
Perhaps the hellhound is a part of a prophecy. In the fanfiction, it could be foretold that a hellhound will either bring great destruction or be the savior of the demigod world. Percy then has to figure out which path the hellhound is on and try to influence it to the side of good if it's the one that could cause destruction.
It also serves as a connection to the gods. In fanfiction, the way a character consumes or interacts with ambrosia might symbolize their relationship with the divine. For instance, if a character is hesitant to eat ambrosia, it could show their distrust or fear of the gods who provided it.
In many fanfictions, he serves as a bridge between different mythologies. Since Percy Jackson is based on Greek mythology and Archangel Michael is from a more Judeo - Christian tradition, his inclusion in the fanfiction can create interesting crossovers. He might introduce new concepts and powers that are foreign to the Greek demigods, which then leads to new character development as they learn to adapt and work with these new elements.
Takara Phoenix could also be a love interest for one of the main characters. In many fanfictions, new characters are introduced to create new relationships. Maybe Takara has a complicated past that draws the attention of Percy or one of his friends, and their relationship develops throughout the story.