Their relationship might develop if they both find themselves in a situation where they are outcasts among their respective groups. They could bond over their feelings of not fully belonging and then decide to create their own place in the High School DxD universe. For example, starting a club for those who want to bridge the gap between angels, devils and fallen angels.
It could also develop through a shared experience like saving someone they both care about. Let's say Issei is in danger. Raynare and Asia both have a connection to him in different ways. By working together to save him, they realize that they can be allies and friends. This could lead to a more positive and collaborative relationship in the future of the fanfiction.
One interesting plot idea could be that Raynare, who has had a change of heart after her initial actions, tries to make amends to Asia. Maybe she teams up with Asia to protect the school from a new, common enemy. This would show their growth and development as characters.
One common theme is Asia's growth. Since she starts as a rather timid character in the original, fanfictions often focus on her becoming stronger. Another theme is her relationships, like her friendship with the main characters.
One way it could develop is if Naruto's ninja training and values from his world conflict with the more flirty and forward nature of the female demons in High School DxD. He might see their behavior as inappropriate or untrustworthy, which would fuel his 'hates women' stance.
The character could develop by constantly using the system to level up their stats. For example, if the system has a feature like a stats page, they could focus on increasing their strength, magic power, and speed. This would make them more capable in battles against the various supernatural beings in the High School DxD world.
In fanfiction, Issei might also develop morally. He could be faced with tough decisions where the line between right and wrong is blurred. This forces him to think about his actions more carefully and develop a stronger sense of justice, rather than just acting on impulse like he sometimes does in the original story.
Issei's character often develops by becoming more powerful. His Boosted Gear evolves, and he learns to control it better. For example, he might gain new abilities or forms in fanfiction.
They might develop their love in high school through shared experiences. For example, they could both be on the school's Pokemon exploration team. Ash's adventurous spirit and Dawn's careful planning would complement each other well. Ash could be the one to rush into dangerous situations, and Dawn would be there to pull him back and come up with a more strategic approach. This mutual reliance could lead to a deeper connection and eventually love. Also, high school parties and dances could be a place where they start to see each other in a different light, like when they share a slow dance and feel a special spark between them.
Well, the story could start with Naruto and Fem Kyuubi being transferred to the High School DxD school. Naruto might struggle to adapt to the different rules and social hierarchy there. The Fem Kyuubi, on the other hand, could use her charm and wits to navigate through the new environment. Their relationship could evolve as they face challenges together, like dealing with the various factions in the school.
I really liked 'Asia's Unlikely Ally'. In this fanfiction, the OC is a transfer student with a special power. The way the author writes the interactions between Asia and the OC is really heartwarming. It also has some exciting action scenes that fit well with the overall High School DxD vibe.
Issei might develop more confidence. If the sunshine in the fanfiction gives him a special power or ability, he could become more self - assured in battles and in his relationships. For example, he may no longer be as hesitant when facing stronger opponents.