There would probably be the billionaire, of course. Then there might be a love interest, who could be from a different social class. There may also be a villain - like character, perhaps a jealous rival in business or someone who wants to take advantage of the billionaire's wealth and relationship.
Well, love is obviously a central theme. In this novel, the love of the billionaire might be betrayed by someone close to him or her, like a partner or a business associate. Betrayal can bring out themes of heartbreak and loss. Also, the story might touch on the theme of social status, as the billionaire's status can both attract and complicate relationships.
There could also be new characters introduced. Maybe a business rival who is jealous of Naruto's success. This rival could be from another village or even an outsider who has his own motives for trying to take down Naruto's billion - dollar empire. And of course, the Hokage would still play a role, as Naruto's actions as a billionaire would have an impact on the village's politics and power structure.
The main characters in a 'love of a billionaire novel' usually include the billionaire. He could be a playboy type who has been through many relationships but never truly fallen in love until he meets the right person. The female lead could be a strong - willed woman, perhaps an artist or a writer, who is not easily impressed by his wealth. Their different personalities and life goals create an interesting dynamic. There might also be secondary characters like the billionaire's business associates or the woman's friends who play roles in either helping or hindering their relationship.
Cinder Fall could be a likely betrayer. She's already a villain in the original series, and in a fanfiction, she could pretend to be an ally to one of the RWBY members only to betray them at a crucial moment, perhaps leading them into a trap set by Salem.
Sasuke could also be a character who is frequently betrayed in these fanfictions. Given his complex personality and his history of being both a loner and a seeker of power, he might be lured into dangerous alliances in the DxD world. And his partners in the DxD world could betray him when they realize they can't control him or when his power becomes a threat to them.
Since we don't have more details about this particular novel, it's hard to say for sure. However, in most novels about being betrayed by love, there is often a central character who experiences the betrayal. This character could be male or female. There may also be supporting characters like friends or family members who either help the betrayed character or are somehow involved in the situation.
Ron is a likely candidate. In the original story, they had their ups and downs, and in fanfiction, it's easy to imagine him doing something that Hermione would see as a betrayal, like not supporting her in her academic pursuits. Another could be Draco Malfoy. He could pretend to befriend her for some devious reason and then turn on her.
Even Ginny could be written as a betrayer in a fanfic. For example, if she becomes possessed by a dark force, she might turn against Harry. Her relationship with Harry is so central in the original story that a betrayal from her would be a huge shock and create a lot of drama in the fanfic.
Obviously, Percy Jackson is the central character. The Olympians such as Zeus, Poseidon, and Athena are likely to be involved as the ones doing the betraying. Other demigods like Annabeth Chase could also be part of the story. She might be torn between her loyalty to Percy and her respect for the Olympians. There could also be minor gods and goddesses who either side with Percy or the Olympians, depending on their own motives and relationships. For example, Hades might see an opportunity to gain more power if Percy is out of the picture, or he could help Percy out of a sense of fairness.
Well, obviously Naruto himself is the central character. Sasuke could be involved as he has a complex relationship with Naruto. In a crossover, if Naruto is betrayed and ends up in the Dragon Ball universe, Vegeta might be a character he interacts with. Vegeta could initially see Naruto as a weakling but later come to respect his skills. Another character could be Luffy from One Piece. If Naruto is betrayed and crosses over to the One Piece world, Luffy would likely befriend him and help him out, seeing Naruto's situation as similar to his own crewmates' struggles.