In this fanfiction, Naruto as Rias' little brother could also have a unique role in the social structure of Rias' world. He might be seen as an oddity at first because of his different powers and origin. However, as time goes on, he earns the respect of others. He could also make new friends among Rias' comrades and together they explore new ways to use their combined abilities in various adventures.
The plot might involve Naruto trying to adapt to the new environment of being related to Rias. Since he has his own strong sense of justice from his ninja world, he could conflict with some of the more underhanded tactics in Rias' world. But in the end, they work together to overcome difficulties. For example, when facing a powerful enemy that neither of them could handle alone, they combine Naruto's ninjutsu and Rias' devil powers to defeat it.
One possible plot could be that Naruto, as Rias's brother, brings his ninja skills to the world of High School DxD. He might use his jutsu to protect Rias and her peerage from various threats, like the devils from other factions or rogue exorcists. And along the way, he could also teach some of his ninja techniques to the members of Rias's peerage.
The plot could involve Naruto using his knowledge of chakra to diagnose Rias' brother's illness. He might discover that it's not a normal sickness but something related to the supernatural nature of their world. For example, his chakra flow could be disrupted by a dark magic spell.
Well, it could be a story full of interesting dynamics. Naruto's energetic and determined personality would contrast with Rias' more composed and strategic nature. Maybe Naruto, as Rias' little brother, would bring a new kind of chaos to the supernatural world she inhabits. He might introduce some of his ninja skills and values into her group, like loyalty and never giving up. It could also lead to some really cool fight scenes where Naruto uses his shadow clones and Rasengan against the devils and other creatures in Rias' world.
Issei could be involved. He might be initially skeptical of Naruto, but as they train together or fight side by side, they become friends. Akeno could also play a part. She might be curious about Naruto's powers and try to learn some of his techniques. Kiba would be another character. Since he has his own combat abilities, he and Naruto could have friendly competitions to see who is stronger in different aspects.
The plot could involve Naruto finding himself in a situation where he has to interact with Rias's brother. The brother, being too involved in his own world of power and politics, simply brushes Naruto off as unimportant. Naruto then decides to prove himself not through grand displays of power, but through his kind heart. He helps those in Rias's group who are being overlooked or underestimated, just like he was in his own village. This catches the attention of Rias's brother who starts to see the value in Naruto he had previously neglected.
Well, one possible plot could be Naruto growing up in the world where Rias lives. He might struggle to fit in at first because of his different upbringing in the Naruto universe. But then, he could use his ninja skills and strong will to protect his sister Rias and her friends. He could also introduce some new ninja - like elements to their world, like new combat techniques or ways of training.
Well, it could be that Naruto somehow gets transported to the world of High School DxD and discovers he has a connection to Rias, like being her long - lost brother. Maybe he uses his ninja skills to protect her from the various threats in her world.
Well, in a 'Naruto is Rias' brother' fanfiction, there would be a lot of potential for character development. Naruto, being from a world where he had to fight for his place and for the safety of his village, would bring that same determination to protect Rias and her friends. He might be shocked at first by the devil society's hierarchy and customs, but would gradually find ways to fit in and make changes. Rias, on the other hand, would have a powerful and loyal brother by her side. They could face off against common enemies, like other devils who oppose Rias' ideas or angels who see Naruto as an unknown and dangerous element. The fanfiction could also explore their family backstory, how they were separated in the first place and what it means for them to be reunited now.
Naruto's powers would be a game - changer. His Rasengan alone could be a very powerful weapon against the enemies in the devil world. His shadow clones could be used for various purposes, like scouting or overwhelming opponents in battle. This would give Rias' side a huge advantage in any conflicts.
One possible plot could be that Naruto and Rias, through some magical or unexpected circumstances, find themselves in a relationship. Their pregnancy could then bring about various challenges. For example, they might face opposition from their respective worlds. Naruto's world of ninjas might not understand his relationship with Rias from a different realm, and vice versa. Their friends and allies would have different reactions, some being supportive while others being skeptical. They would also have to deal with the practical aspects of preparing for a baby, like finding a safe place to live and ensuring the child's future in two very different and complex worlds.