It could be developed by having Naruto's emotionless nature be a result of some sort of curse or magic that crossed over from his own world to the High School DxD world. His journey could then be about trying to regain his emotions while also dealing with the various challenges in this new universe. He might not be as easily swayed by the temptations or manipulations of the different factions because of his lack of emotions.
One way it could be developed is by exploring how Naruto's emotionless state affects his interactions with the characters in the High School DxD world. For example, his lack of emotions might make him seem like an enigma to the devils, angels, and fallen angels. He could approach battles in a very cold and calculated way, which would be different from his usual passionate self in the Naruto universe. This could lead to interesting alliances and rivalries.
The story could start with Naruto suddenly finding himself in the High School DxD world in an emotionless state. Since he doesn't show emotions, it could make it difficult for others to understand his motives. This would create a lot of misunderstandings. However, as the story progresses, he could gradually start to show glimmers of his old self as he forms bonds with certain characters like Issei or Rias. These new relationships could be the key to unlocking his emotions again.
One way could be through the power system. The EMS (Eternal Mangekyou Sharingan) from Naruto could be a unique power that a character in the High School DxD world acquires. Maybe a transfer student from a hidden ninja village arrives at the high school and has to keep their EMS a secret while dealing with the devils and angels in the school. This could lead to some interesting battles and interactions as the powers of the EMS, like the ability to use powerful jutsus, contrast with the magic and abilities of the High School DxD characters.
He could be seen as a mysterious figure at first. Given his different appearance and abilities compared to the devils, angels, and fallen angels in the DxD world. Naruto might initially be a target of suspicion, but as he shows his good heart and helps out in various situations, like protecting the school from an attack, he would gradually be accepted. He could also have some interesting interactions with the magic and power systems in the DxD universe, maybe even finding a way to combine his chakra with their powers.
Naruto could fit in as a new transfer student in the High School DxD universe. His out - of - this - world ninja skills would make him stand out immediately. He might initially be confused by the supernatural elements but would quickly adapt and use his skills to protect the school or his new friends from any threats.
One possible fanfic could be about Naruto being transferred to the High School DxD universe and his encounter with the Juubi there. Maybe he has to team up with the characters from High School DxD to deal with the threat of the Juubi. For example, Naruto's unique abilities like the Rasengan and Shadow Clone Jutsu could be a great asset in battles within this new universe.
Naruto Otsutsuki could fit into the High School DxD universe by being a new and powerful entity. His abilities would be a significant addition. For instance, his transformation abilities like the Nine - Tailed Fox form could make him a force to be reckoned with among the devils, angels, and fallen angels in the DxD world.
He would still likely have his chakra - based powers from the Naruto universe. So he could use techniques like the Rasengan or Shadow Clone Jutsu. However, due to his emotionless state, he might use them in a more precise and less flashy way. His Nine - Tails chakra could also be present, but perhaps he would have better control over it since emotions often cloud his control in the original series.
One possibility could be a story where Naruto, with his unique abilities from his own world, enters the High School DxD universe and meets Kuroka. In this harem fanfiction, Naruto's kind heart and strong power might attract Kuroka and other characters. They could go on adventures together, with Naruto's ninja skills being a novelty in the DxD world. And his determination to protect could make him a central figure in the harem.
Sure. Many fanfiction enthusiasts enjoy creating crossovers between different popular franchises. Naruto's Rinnegan gives him abilities like the Six Paths powers which could be really interesting to see in the context of High School DxD. If Naruto in this fanfiction is modeled after Pain in some ways, perhaps he would have a more complex and darker view of the world in the High School DxD setting. He might use his powers in ways that are different from how Naruto usually does in his own series. For example, he could use his Rinnegan powers to manipulate the power dynamics between the different factions in High School DxD, like the devils, angels, and fallen angels. This kind of fanfiction would surely attract readers who are fans of both series and are looking for a fresh take on their favorite characters.
Asta could be brought into the High School DxD fanfic as a result of a multiverse - related event. In this case, different universes are colliding or being connected in some way. His presence would disrupt the power balance as his anti - magic is something that no one in the High School DxD world has really encountered before. He could end up training with the devils to learn more about their magic while also teaching them about the concept of anti - magic.
In the High School DxD universe, Naruto's chakra might be seen as a new form of energy. His Sage Mode would give him enhanced senses and strength. He could detect the presence of devils and angels from afar. When using Sage Mode, his attacks would be even more powerful. For example, a Sage Mode - enhanced Rasengan could cause massive damage to the toughest of opponents in the DxD world.