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.
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.
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.
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.
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.
Sasuke and Magneto. Both are complex characters with a bit of a dark side. They could either become enemies as their goals might clash. Sasuke is on a journey to gain power for revenge, and Magneto wants to protect mutants but sometimes uses extreme methods. Or they could form an unlikely alliance, learning from each other's determination and power - seeking motives.
Probably Wolverine and Spiderman. Wolverine is often on the front lines in X - Men stories, and his no - nonsense attitude would contrast well with Spiderman's quippy nature. They might meet when investigating a strange occurrence in New York that involves both mutants and non - mutants.
In a fanfiction, the characters' personalities would greatly influence their interactions. Percy is a bit of a rebel and a free spirit, which could either clash or mesh well with the more structured Avengers. Thor, being a god - like figure in his own right, might recognize the power and divinity within Percy and the other demigods. They could share stories about their respective mythologies. Natasha Romanoff could take an interest in the demigods' combat training, which is different from her own. She might learn some new fighting techniques from them, while also teaching them some of her stealth and espionage skills.
It could be Percy and Black Widow. Natasha is a master of reading people, and she'd notice Percy right away. She might approach him in a more stealthy way compared to the others, trying to assess if he's a threat or an ally. And Percy, being used to danger, would be on his guard at first, but then start to trust her as she shows her good intentions.
Percy Jackson himself would be a likely survivor. His powers over water, his combat skills, and his ability to think on his feet would give him an edge. Annabeth Chase would also be a strong contender. Her intelligence and strategic thinking would help her navigate the challenges. Also, Katniss Everdeen from The Hunger Games. She is a skilled archer and survivor, so she could hold her own against the demigods and the other threats in the crossover arena.
One character that could betray Percy is Thalia. She has her own issues with the gods and her place in the world. Maybe she gets jealous of Percy's growing popularity and power among the demigods. So, she decides to side with an enemy to take Percy down a notch. Additionally, some minor characters that Percy has helped in the past could be the ones to betray him. They might feel indebted to him but also resentful at the same time. An enemy could manipulate their feelings and turn them into traitors against Percy.