The interaction between Illya and Koneko could be fascinating too. Koneko is a quiet and strong fighter. Illya's bubbly and sometimes clumsy nature could break through Koneko's stoic exterior. They could bond over things like their love for food or their determination to protect their friends, despite coming from very different backgrounds.
The interaction between Illya and Rias would be really interesting. Rias is a powerful devil with a lot of charm and leadership. Illya, on the other hand, is a magical girl with her own set of powers. They could start off as rivals, both vying for the attention or respect of other characters, but then realize they have more in common and can work together.
The interactions between Naruto and Akeno would be quite fascinating. Akeno has her own allure and power. Naruto, being godlike, would be an enigma to her. She might be intrigued by his powers and his different way of looking at things. They could have some deep conversations about power, morality, and the differences between their two worlds while also having some light - hearted moments due to Naruto's sometimes clueless nature about the more flirty aspects of Akeno's personality.
Definitely Naruto and Issei. Issei is all about his perverted ways and getting stronger, while Naruto is focused on protecting his friends and achieving his dreams. Their clash of personalities would be really interesting. Naruto might not understand Issei's obsession with girls at first and try to set him straight. And Issei would be amazed by Naruto's power and want to learn from him.
Natsu and Akeno could have some fun interactions. Akeno has her own brand of mischief, and Natsu might not be used to her teasing ways. Their first meeting could be full of misunderstandings, with Natsu thinking she's an enemy at first because of her devious appearance, but then realizing she's an ally and developing an interesting friendship.
Itachi and Rias would be really interesting. Rias is used to being in control and having power, but Itachi's calm and collected nature along with his overwhelming power would put her in a different position. She would likely be intrigued by his Sharingan and his combat abilities. Itachi, on the other hand, would be dealing with a different kind of power structure and would have to navigate the social hierarchy of the devils in Highschool DxD.
Another interesting interaction could be between Naruto and Akeno. Akeno is known for her mischievous nature. When she meets Naruto, she would be curious about his ninja skills. Maybe she would try to play some pranks on him using her magic, but Naruto, with his quick reflexes and shadow clone jutsu, would be able to turn the tables on her. This would lead to a really fun and dynamic relationship between the two characters.
Ruby and Issei would be an interesting pairing. Ruby's innocent yet determined nature combined with Issei's perverted but also heroic side could lead to some really fun and dynamic interactions. They could learn a lot from each other in terms of combat and dealing with different types of threats.
Definitely Naruto and Issei. Issei is all about perverted thoughts and power - seeking, while Naruto is more about friendship and protecting his comrades. Their interactions would be full of contrasts and they could learn a lot from each other.
Maybe in the fanfiction, there's a magical event that links the world of Illya with the Highschool DxD universe. Illya's innocent nature could be a contrast to the more risqué and wild nature of some of the Highschool DxD characters. Her friendship with Issei could start off rocky but then develop into a strong bond as they train together to improve their respective powers.
Ichigo and Issei would be really interesting. Ichigo, with his calm and collected nature most of the time, compared to Issei's more pervy and hot - headed ways. Their different personalities could lead to some really funny and intense interactions, especially when it comes to fighting side by side or arguing about battle strategies.
Ron Weasley and Issei Hyodo could also be a fun pairing. Ron's laid - back but brave nature along with his Weasley family magic could interact interestingly with Issei's determination and his unique Sacred Gear abilities. They might start off as rivals, but then become friends as they face common enemies in the combined universe of the fanfiction.