In fanfiction, the connection between Percy Jackson, Ares, and Alsh High School could be really interesting. Ares is the god of war, and Alsh High School could be a place where he wants to stir up some chaos. Percy, on the other hand, is often in the business of restoring order. So, perhaps Ares is using the school as a battleground of sorts, with students unknowingly caught in the middle. Percy would then have to navigate the high school's social and physical environment to face off against Ares and protect the innocent students.
Ares could be the antagonist. He might be there to create conflict among the students, like starting rivalries or fights. Maybe he's looking for a particular student with special abilities for his own devious plans.
Characters like Annabeth could be developed by exploring her jealousy or concern when Percy is spending so much time at Ares High School. She might try to infiltrate the school in some way to keep an eye on him. And for the Ares - influenced characters, you can show their internal conflict between following Ares' brutal ways and their own sense of right and wrong as they interact more with Percy and his friends.
Perhaps there's a mystery at Ares High School where strange things keep happening, like students getting sudden bursts of uncontrollable strength. Percy, suspecting it has something to do with Ares, investigates and discovers an ancient artifact hidden on campus that's causing the chaos. He then has to find a way to stop it without getting caught by the school authorities or Ares' minions.
In fanfiction, the relationship could be developed by exploring their family ties. Since Percy is a demigod and Ares is a god, there could be some underlying connection through the divine family tree. Maybe they discover that they are related in a more distant way than they thought. This could lead to Ares having a more protective side towards Percy, or Percy seeing Ares in a less antagonistic light. Also, they could be forced into a situation where they have to communicate their feelings and motives clearly, like being trapped in a magical prison together. This would make them open up and start to build a more complex relationship.
In Percy Jackson fanfiction, Ares is often portrayed as a very aggressive and war - hungry figure. He might be shown as having a short temper and being quick to anger, much like his depiction in the original series. For example, he could be seen starting battles or conflicts just for the sake of it, and his followers might be depicted as equally bloodthirsty.
First, know your characters well. Percy's personality traits like his loyalty and his ADHD - influenced impulsiveness should be maintained. Then, create a high school setting that can incorporate the mythological elements. For example, a history class could be about Greek mythology. Plot - wise, think of how the demigod problems would translate to high school issues, like bullies could be monsters in disguise.
Most of the gods would be confused at first. Hera might see it as an opportunity to manipulate the situation for her own ends. She could try to use Percy's new connection to Ares to create more chaos or to further her own plans. Poseidon would be very conflicted. On one hand, he has a connection to Percy as his son, but now Percy has this new link to Ares which could put Poseidon in a difficult position among the other gods.
He might focus on his training. Percy could use the time alone to practice his sword - fighting skills or improve his control over water. This would not only keep him occupied but also make him more powerful.
Well, in some fanfictions, they might connect through the concept of magic. Since both Fairy Tail and Percy Jackson deal with magic in their own ways. The 'god soul' could be a concept borrowed from Percy Jackson's world of gods and demigods and be incorporated into the Fairy Tail universe in the fanfiction. Maybe a character in the fanfic has a god soul which gives them special powers similar to the magic in Fairy Tail.
One great Percy Jackson high school fanfiction is 'New Beginnings at Goode High'. It shows Percy trying to fit into a normal high school life while still having his demigod secrets. The author does a great job of portraying the internal struggle Percy faces between his two worlds.