Well, considering the nature of 'highschool dxd', characters like Xenovia could be involved in the 'ultimate hypnotism fanfiction'. Her strong will and combat skills might make her a target for hypnotism to be subdued or she could be the one trying to resist hypnotic control. Also, Asia, with her kind and gentle nature, could be a character that gets caught up in the hypnotism plot, either being hypnotized to do things against her will or being the one to break free from it and help others.
Well, 'highschool dxd' is a popular anime. In the context of 'ultimate hypnotism fanfiction', it could be about using hypnotism in the 'highschool dxd' universe in ways that the original story doesn't. It might involve characters using hypnotic powers for various purposes, like getting information or influencing others' actions. Fanfiction often takes the existing world and characters and twists them in new and interesting ways.
Issei is often involved as he is one of the central characters in the Highschool DxD universe. His character can be greatly influenced by hypnosis, either being the one using it or being affected by it.
Rias herself is sure to be a central character. Issei will also be very involved, as he has a close relationship with Rias. Her peerage members like Akeno, Koneko, and the others are likely to play important roles too. And of course, there may be appearances from other important figures in the Highschool DxD universe, such as the leaders of different devil clans.
Akeno would also be a likely character. She is often involved in Issei's affairs and has a flirtatious relationship with him. She might tease Issei about the chastity belt at first but then also use her knowledge and powers to assist. Kiba could be another one. As Issei's friend, he would offer his support and might even be involved in some sort of quest to find a solution for the chastity belt problem.
Obviously, Escanor is a main character. He is often the center of the story due to his powerful presence. In addition, characters from the original Highschool DxD like Issei might also be involved. Issei could be a friend or a rival to Escanor in the fanfiction, adding an interesting dynamic as Issei is known for his own growth and development in the original series.
Issei is often a central character in these fanfictions. Since he is the main protagonist in the original series, his relationships and potential betrayals are explored. For example, a situation where his friends or allies in the Occult Research Club turn against him for some reason, like jealousy over his growing power or a misunderstanding about his actions.
Issei is often involved. Since he has a connection to the Gremory family through Rias, his actions and decisions can sometimes be a part of the Gremory - bashing scenarios. Another could be Sona, as her family has a relationship with the Gremorys and she might be in a position where she has to take a stance against them in some fan - created situations.
Issei is a likely candidate. His over - the - top perverted nature could be a target in bashing fanfiction. Some might write stories where his actions finally catch up with him and he has to face the consequences of constantly objectifying women.
Rias Gremory could also be a main character. Her relationship with Issei and her role as a devil leader means she can play a crucial part in fanfictions about the One Winged Angel. She might be involved in helping Issei master the form or dealing with the consequences of its appearance.
Naruto and Issei are very likely crossover characters. Naruto, with his strong will and powerful ninja skills, would be an interesting contrast to Issei, the perverted but also determined protagonist of Highschool DxD. Another likely pair could be Sasuke and Vali. Both are brooding, powerful characters with their own agendas. Sasuke's Sharingan abilities could have some really cool interactions with Vali's powers in the context of this fanfiction. And of course, Kakashi could be a great crossover with some of the more strategic characters in Highschool DxD, like Sona, as he is known for his intelligence and combat skills.