Well, it would be quite an interesting relationship. Naruto's strong will and combat skills from his own world could mesh well with Rias' leadership in the Highschool DxD universe. He would likely bring a new sense of loyalty and determination to her peerage. Also, his ability to make friends easily might help him fit into the complex social structure of the DxD world.
The development of their relationship would also depend on how the fanfiction writer chooses to handle the power dynamics. Naruto is extremely powerful in his own right, and Rias is a powerful devil. They could either become a power couple, using their combined strength to face any threats, or they might face challenges due to differences in their power sources and how they are perceived in their respective worlds. Naruto's chakra-based powers are very different from Rias' devil powers, and this could create both conflict and opportunities for growth in their relationship.
He might react with hostility. Dark Naruto has a certain edge to him, and if he sees Rias as a threat or someone he doesn't like, he'll likely oppose her. He could use his combat skills to challenge her directly.
Naruto could bring a lot of energy and a new fighting style. His ninja skills would be a unique addition. For example, his shadow clone jutsu could be used for various strategic purposes in battles against other peerages. His positive and determined attitude would also be contagious, inspiring Rias' other servants to be more bold and confident.
Their relationship could develop further through shared challenges. For instance, if they face a really tough opponent together, they'll learn more about each other's strengths and weaknesses, and that can deepen their bond. Another way is through communication. If Issei starts to open up more about his insecurities and Rias does the same, they can become closer on an emotional level.
The relationship between Issei and Rias would evolve in a beautiful way. They would be each other's support system. Issei, who has always been passionate, would become more refined in his love for Rias. Rias, on the other hand, would become more lenient towards Issei's sometimes - rash decisions. They would have a relationship based on mutual understanding, respect and love. Their engagement would be the starting point of a long and fulfilling journey together, filled with love, laughter and some tears as they face the challenges of their world.
It could start with them being forced to work together on a mission. At first, they might clash due to their different personalities. Issei is more impulsive and Yubelluna is more reserved. But as they face difficulties during the mission, they start to understand each other better. For instance, when Issei rushes into a fight without a proper plan, Yubelluna scolds him but also helps him out. This back - and - forth gradually turns into a more affectionate relationship.
Naruto's development could be centered around his ability to adapt to a new culture. The Highschool DxD world has its own set of rules, ethics, and social norms. He would need to learn and respect these while still maintaining his own identity. His sense of justice might also be challenged as he realizes that the good - bad divide in Highschool DxD isn't as clear - cut as in his own world. This could lead to him re - evaluating his beliefs and growing as a character.
Their relationship could start as comrades in arms. As they face challenges together, they begin to respect each other's skills. Then, gradually, they might develop a friendship based on mutual trust. Eventually, it could turn into a romantic relationship as they discover more about each other's personalities and what they truly care about.
For the male OC, you can start by giving him a distinct personality trait. For example, if he's really shy, it can create interesting interactions with Rias who is often more confident. This shyness could be due to his insecurities about his newfound powers or his place in the supernatural world.
They could become friends. Naruto, with his friendly and open - minded nature, would be interested in Rias and her world. Rias, in turn, would be attracted to Naruto's strength and determination. They might start training together, sharing their combat techniques.
Naruto would likely become very distrustful. After being betrayed by Rias, he would find it hard to trust anyone else in the Highschool DxD world. This could isolate him and make his journey much more difficult as he would be on his own without allies.