In a fanfiction, Sona's brother could be a mentor figure. He might teach Sona some ancient and powerful magic that has been passed down in their family. He could also be a bit of a rebel, going against the traditional ways of the devil society. For instance, he might believe in more equal relationships between devils and other races, like angels or humans, which could cause some conflict within their family and among the other devils.
One possibility could be that Sona's brother is a powerful figure in the underworld. He might be involved in political intrigue within the devil society. For example, he could be trying to form alliances with other noble devil families to increase the power and influence of Sona's family. Maybe he has some special abilities that are yet to be discovered by others, which he uses to his advantage in the complex power dynamics of the Highschool DxD world.
Perhaps Sona's brother has a tragic past. He could have lost someone he loved dearly in a war between devils and angels. This event could have shaped his personality and goals. He might be on a quest for revenge or trying to find a way to prevent such tragedies from happening again. His relationship with Sona could be complex, as he wants to protect her from the same pain he has endured, but also knows she needs to grow strong in the dangerous world they live in.
Sona's brother might be an innovator. He could be introducing new ideas and technologies to the devil world. Maybe he has a vision of a more modern devil society that is more in line with the human world. He could be working on projects like creating new magical devices or new forms of devil contracts that are more fair and beneficial for both parties. This could put him at odds with the more conservative elements of the devil community.
One possible fanfiction could be about Rias and Sona teaming up for a school event. They might put aside their usual competitiveness and work together to organize a devil - related festival at the school. They could combine their unique skills and powers to create an amazing event that not only impresses the other students but also strengthens their bond as friends.
One way is to explore her family background more. For example, showing how her upbringing in the devil society influenced her leadership style in the student council.
A fanfiction could show how Rias and Sona first became friends. Maybe it was during a difficult time at school when they both had to face some sort of discrimination from other devils because of their different leadership styles. They found comfort in each other and decided to support one another from that moment on.
A third plot idea might be Sona trying to modernize the traditions of the devil world within the context of the school. She could face opposition from more conservative devils, and the story could explore her struggle to bring about change while still maintaining her position and respect.
Power - up themes are also common. Naruto already has his powerful ninja abilities, and when combined with the magic and power systems in High School DxD, there are often scenarios where he or Sona gain new powers or find new ways to use their existing ones. For example, Naruto might learn to combine his chakra with Sona's magic for a super - attack. Another theme is friendship and alliance. Since they are from different worlds, they need to form an alliance to face common enemies. This often leads to the development of a deep friendship between them as they rely on each other's strengths.
Friendship is a common theme. Tsubaki and Sona often start with a pre - existing friendship in the fanfictions and it either deepens or is tested. For example, they might have to support each other through tough times at school or in the supernatural world.
In this fanfic, Naruto could bring his sense of justice to Sona's side. Since Naruto is always about protecting his friends and doing what's right, he could inspire Sona and her followers. His chakra could be an interesting element in the world of devils and angels. He might even find a way to use his chakra to enhance the abilities of Sona's peerage members.
Yes, there are quite a few. You can find them on various fanfiction websites. Some focus on their relationship developing gradually as they face different challenges together in the Highschool DxD universe.
Perhaps Alex Black has a mysterious past that Sona is intrigued by. They could start off as acquaintances, but as time goes on, they form a deeper bond over shared interests in magic and the supernatural world of Highschool DxD.