Akeno would also be an interesting character for Percy to interact with. She has a mysterious and alluring personality. Percy, who is used to dealing with the goddesses in his world, would find Akeno's charm and power both familiar and yet different. Their interactions could involve Akeno trying to tease Percy, while Percy tries to stay focused on his own goals in the DxD world, and this could lead to some really engaging and sometimes tense moments between them.
Issei would be really interesting. He's the main character in DxD and has his own set of powers and a rather unique personality. His pervy nature would contrast with Percy's more heroic and sometimes serious demeanor. Their interactions could be both comical and lead to some great character development for both.
Draco Malfoy would be a likely character. Given his Slytherin status, he would likely have a complex relationship with Percy. He might start off as hostile, seeing Percy as an outsider, but then they could end up having to work together for some reason.
Grover might also be involved. His ability to sense emotions and his connection to nature could play a role. He could be the one to initially sense Padme's arrival or help her understand the more magical and nature - related aspects of the Percy Jackson world, like the power of the gods and the spirits of the forest.
Percy himself, of course. Given his leadership skills and powerful abilities, he would be the first to step up and face the Pillar Men. His ability to control water could be a great asset or a hindrance depending on the situation.
Annabeth, if she were with Percy, would be more interested in the architecture and strategic planning of Troy. She could offer her knowledge to the Trojans or the Greeks, but they might not trust her either. And Percy would have to protect her from those who might see her as a threat or a sorceress.
Percy would probably be very cautious around Morathi at first. Given his experiences with tricky and powerful beings, he'd be on guard. Morathi, being the conniving character she is, might try to charm Percy or manipulate him. For example, she could use her allure to make Percy lower his defenses, but Percy's loyalty to his friends and his own sense of right and wrong would likely make him resist.
A character like Circe could be really interesting to pair with Percy. Circe has her own magical powers and a connection to the more mysterious parts of the mythological world. Percy could learn a lot from her about magic and how to use his powers in different ways. Also, the dynamic between them would be full of tension and intrigue, as Circe might be tempted to use Percy for her own ends. Another great pairing would be Reyna. Reyna is a strong and independent leader, and when paired with Percy, they could lead different groups of demigods in a joint mission. Their leadership styles would clash and mesh in interesting ways, and they could develop a deep respect for each other as they face challenges related to Percy's underworld heritage.
Azula would probably try to use Percy at first. She might see his powers as something she could control or use for her own gain. However, Percy is not one to be easily manipulated. He would resist her attempts, which could lead to some intense verbal sparring between them. As time goes on, they might develop a grudging respect for each other. For example, Percy might admire Azula's strategic mind, and Azula could respect Percy's loyalty to his friends.
Well, Annabeth would definitely be one. She's always been by Percy's side, and in this fanfiction, she might be a bit worried about Percy being the champion of Nyx. She could be trying to help him while also being cautious of Nyx's motives.
He would surely interact with Annabeth. Their relationship is central in the Percy Jackson series, so in a Tartarus fanfic, she'd likely be there to support him or be in a similar situation as him.
The settings are quite different. Percy Jackson often has settings like Camp Half - Blood, which is a place full of demigods training and living. In Highschool DxD, it's mainly set in a high school with a lot of supernatural beings. In fanfiction, they could interact in a way that the Highschool DxD characters visit Camp Half - Blood. They would be introduced to the Greek demigod way of life, and it could lead to some really interesting cultural clashes and exchanges of power.