Well, it could be related to a power struggle. Suppose there's a limited resource in their fictional world, like a special type of chakra or magical item. Naruto and Rias both need it for their own reasons. Rias, being more desperate, decides to hurt Naruto to get to it first. Or perhaps Rias has some sort of loyalty to a group or a cause that Naruto unknowingly opposes, and she sees him as a threat to that loyalty. So, in order to protect what she believes in, she ends up hurting him.
One possible reason could be a misunderstanding. Maybe Rias mistakes Naruto for an enemy due to some misinformation. For example, if there's a false rumor that Naruto is planning to attack her group. Another reason might be that Rias is forced to hurt Naruto under some sort of mind control or external pressure. It could also be a situation where Naruto accidentally gets in the way of Rias while she's dealing with a more powerful threat and she has no choice but to harm him in the process.
In the context of fanfiction, it could be a character - development - driven plot. Rias might start off as a good - intentioned character but something in her past or her nature is gradually revealed. Maybe she has a dark side that gets triggered when she meets Naruto. For instance, Naruto's positive and carefree attitude might remind her of someone she hates from her past. This could lead her to lash out and hurt Naruto. Also, it could be part of a bigger plot where Naruto's hurt is a catalyst for other characters to come together, either to seek revenge or to find a way to heal him and in the process, there are new alliances and story developments.
Maybe it's because of the different power systems. Naruto has chakra and his ninja abilities, and Rias has her devil powers. If in the fanfiction these power systems are not properly integrated or if one overshadows the other in an unappealing way, Naruto could be depicted as hating Rias. Say, if Rias' devil powers are made to seem too overpowering and it goes against Naruto's sense of fairness in combat, it could lead to such a scenario.
In the 'naruto rejects rias fanfiction', Naruto might reject Rias because of their different character traits. Naruto is known for his boisterous, positive, and somewhat naive nature. Rias, as a devil in her own story, has a more complex and often manipulative side. Naruto, with his straightforward ninja values, might not be able to deal with or accept Rias' way of doing things. For example, Naruto believes in hard work and loyalty among his comrades, while Rias' actions might be driven more by power plays and strategic considerations within her devil society, which Naruto could find unappealing.
One possible reason could be a difference in their goals. Naruto is from the Hidden Leaf Village with a mission to protect it and promote peace there. Rias, on the other hand, has her own responsibilities in the Underworld. Their conflicting duties might lead to Naruto leaving.
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.
Perhaps in this fanfiction, Naruto has lost his way in his own world and somehow ends up in Rias' realm. Rias, being kind - hearted, adopts him. Naruto would have to adapt to a whole new set of rules and powers. He might face challenges from other groups who are suspicious of this new addition, but with his ninja spirit, he overcomes them.
In such a fanfiction, perhaps Naruto is in a new world where Rias, for some reason, completely ignores him. Maybe it could lead to Naruto feeling isolated and having to find his own way in this strange new place. He might start training alone and discover new powers out of his need to prove himself despite Rias's neglect.
Well, it could start with Naruto somehow ending up in the world of High School DxD. Rias might discover Naruto and see his potential, then make him her familiar. The plot could involve Naruto learning about the devil society and using his ninja skills to protect Rias and her peerage.
One possibility is that Naruto is summoned to Rias' world through some sort of magical ritual gone wrong. Once there, he forms an unlikely alliance with Rias. Naruto's chakra - based powers could be a great asset to Rias' team. They might start training together, with Naruto teaching the devils about chakra control and Rias showing Naruto some of the unique magic in her world.
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.
Well, one possible plot could be that Naruto, as the son of Rias, discovers his unique heritage and has to deal with the expectations that come with it. He might struggle to balance his ninja skills with the devil - like powers he inherits from Rias. Maybe he uses his Naruto - like determination to bridge the gap between the ninja world and the world of devils.