One possible plot twist could be that Percy has to hide his true parentage from his friends at Camp Half - Blood. Since Lycaon was a werewolf - like figure and Lupa is associated with wolves in Roman mythology, Percy might have some wolf - like abilities that he doesn't understand at first. For example, he could have enhanced senses like better smell and hearing, which could make him seem different from other demigods. Another plot twist could be that there are other characters who are secretly aware of his true parentage and are either trying to protect him or use him for their own purposes.
A plot twist could be that Percy's connection to Lycaon and Lupa causes him to be shunned by some of the Greek gods. Since his parentage is more related to Roman mythology, the Greek gods might see him as an outsider or a threat. This could lead to Percy having to prove himself in a different way than other demigods. He might have to go on a special quest to gain the acceptance of the Greek gods. Also, his wolf - related abilities could attract the attention of some dark forces in the mythological world who want to use his power for evil.
Well, a plot twist could be that Percy's connection to Tartarus gives him the ability to control the very essence of the underworld. This means he can manipulate the shadows and the dark magic there. But because of his Lupa heritage, he also has a strong sense of loyalty and pack mentality. So, he forms an unlikely alliance with some of the more 'civilized' monsters in the underworld who also follow a code of honor. His friends from Camp Half - Blood are initially very skeptical and even a bit scared of him, but as they learn more about his new powers and how he's trying to use them for good, they start to come around.
One idea could be Percy having to face challenges specific to being the 'son of Lycaon'. For example, he might struggle with the werewolf - like instincts that come with that heritage. He could have to prove himself to the other demigods who are skeptical of his newfound origin.
In this fanfiction, there might be a lot of focus on Percy's relationship with the other wolves in Lupa's pack. He could learn their ways of survival, their hierarchy, and how to be a part of their community. This would be a great way to explore his adaptability and growth.
For his relationship with the Roman demigods, it could be more complex. Since his parents are related to Roman mythology, the Roman demigods might expect him to side with them more. But Percy has his own values and friendships in the Greek side. This could lead to some tension. His relationship with Chiron would also change. Chiron would need to figure out how to train Percy with his new - found abilities. He might have to seek advice from other sources, like some Roman centaurs perhaps.
Lupa herself would be a major character. She's the one who has a special connection to Percy in this story. She could be guiding him, testing him, or having her own motives that are intertwined with Percy's journey.
The setting of the story might shift a bit. Instead of always being at Camp Half - Blood or on quests related to the Greek gods, Percy could be in the territory of the wolves. There could be new threats and challenges there, like rival wolf packs or ancient enemies of Lupa. And all these elements would make for an exciting and different take on the Percy Jackson universe.
To develop his character further, he could start to have visions or dreams related to Lycaon's past. These could be a source of both knowledge and inner turmoil. He could learn about the mistakes Lycaon made and be determined not to repeat them. At the same time, he might discover some long - lost powers or abilities that Lycaon had, and struggle to master them in a way that is true to his own character.
Maybe Percy discovers a prophecy that involves both his father Poseidon and Lupa. He has to journey to different realms under the sea and in the Roman wolf - related places. Along the way, he meets new demigods and creatures that either help or hinder him in fulfilling the prophecy.
A prevalent theme is isolation. In many fanfictions, Percy feels alone because of his strange heritage. He doesn't quite fit in with the normal demigods. Also, the theme of destiny often comes up. He has a special destiny due to his parents that he is constantly striving to fulfill.
I've read a fanfiction where Percy is the son of Lupa and Chaos and it focuses on his relationships. 'Percy's Bonds' is the name. It shows how his different heritage affects his friendships and romances, and how he has to come to terms with who he really is in the context of his relationships.