A possible plot twist is that the characters from High School DxD initially underestimate Naruto due to his neglected state. But then they find out that he has a deep understanding of loyalty and friendship from his time in Konoha. This makes him form unexpected alliances in the DxD world, like teaming up with Issei to take on a common enemy that neither could face alone.
In 'Twisted Fates', the plot twist is that the powers of Ichigo and a certain devil in High School DxD get merged accidentally. This leads to a new form of power that no one expected. It causes a huge shift in the power balance and makes both the allies and enemies of the characters scramble to adjust to this new situation. This fanfiction then delves into how they all cope with this unexpected development.
Well, perhaps a plot twist could be the mixing of the two worlds' forms of magic. Naruto's world has its own kind of jutsu - based magic, while High School DxD has demonic and angelic magic. If these magics were to merge in some characters, it would create really unique abilities. For instance, a character could use a jutsu while also having the ability to summon angels or devils. Another interesting plot twist could be that the Nine - Tails (from Naruto) somehow gets involved in the Rating Games in High School DxD. It would be a huge advantage or a major disruption depending on how it's handled. And what if a character from High School DxD learned the Shadow Clone Jutsu? They could use it for all sorts of mischief or strategic advantages in their own world.
Well, one interesting plot twist is when the Nine - Tails in Naruto is somehow linked to a powerful devil in Highschool DxD. Imagine the chaos and new power - sharing or battling that could occur. It completely flips the script on how we see both the Naruto and Highschool DxD elements. Also, there could be a plot twist where the power - leveling system in Highschool DxD is reversed for Naruto characters, making them struggle in a new way and forcing them to adapt in unexpected ways.
One interesting plot could be Naruto being transported to the High School DxD world and having to adapt to the different rules about magic and devils. He might use his ninja skills in unique ways, like using his shadow clone jutsu in battles against devils or fallen angels. Another plot could involve Naruto teaching some of the DxD characters about chakra and how to use it, which would completely change the power dynamics in that world.
One plot idea could be that Naruto is summoned to the High School DxD world by a powerful magic user who mistakes him for a powerful demon. Once there, Naruto has to prove that he is not a threat while also trying to find a way back home. Along the way, he befriends some of the students at the school and helps them with their own problems, like protecting the school from a sudden attack by a group of rogue devils.
A plot idea could be that some of the devils in High School DxD want to learn the secrets of chakra from Naruto. So they kidnap him to their world. Naruto then has to find a way to escape while also dealing with the political intrigue among the devils, angels, and fallen angels. Another idea is that Naruto's shadow clones could be mistaken for some new type of summoned creatures in the DxD world.
One interesting plot twist could be Naruto having to adapt to the unique magic system in Highschool DxD. Since Naruto has his chakra-based powers, seeing him struggle or find new ways to use his skills in a world of magic would be cool. For example, he might combine his shadow clone jutsu with some DxD magic to create a new and powerful technique.
In some fanfics, a great plot twist is when Ichigo's Hollow powers are misinterpreted by the DxD characters as some sort of devilish power. This leads to a lot of misunderstandings and conflict at first. Another interesting plot twist can be when Ichigo somehow ends up being related to an important figure in the DxD world through some convoluted backstory.
One possible interesting plot could be that Naruto, with his unique ninja skills, gets transferred to High School DxD's world. He might initially struggle to adapt to the different rules and magic there. For example, he could mistake a devil's magic for some kind of new jutsu. Then, he could end up teaming with Issei and his group to fight a common enemy that threatens both the ninja world and the world of High School DxD. Maybe an ancient evil that wants to use the power of both chakras and devil magic for its own dark purposes.
A great plot could be a tournament - style story in the 'Naruto x Rias High School DxD' fanfiction. The tournament could be a mix of ninja and devil skills. Naruto enters representing his ninja heritage and Rias enters on behalf of the devils. Along the way, they have to face opponents from different factions. As they progress, they start to understand each other better and develop a deeper bond. Naruto's determination to win for the sake of his new friends in the DxD world and Rias's desire to prove the strength of the devils would drive the story forward, and their combined efforts could lead to an unexpected victory.