His powers might enhance his attractiveness to the demon harem. For example, his chakra could be something that the demons find alluring. Or his shadow clone jutsu could be used in creative ways, like having clones interact with different members of the harem simultaneously.
In fanfiction about Naruto and Demon Slayer with magic, one interesting aspect is the potential for new power - ups. For instance, a character could combine the Sharingan from Naruto with a Demon Slayer's special vision ability and create a super - powered form of sight. Also, the magic could be used to explain some of the more mysterious elements in both series. Maybe the curse marks in Naruto are actually a form of suppressed magic, and in the fanfiction, a character figures out how to fully utilize this magic, taking on a new and powerful form inspired by Demon Slayer's demon - slaying forms.
Magic in this type of fanfiction can be used to bridge the gap between the two universes. It can make the transition of characters from one world to another more believable. For example, if Naruto characters enter the Demon Slayer world, magic could be the reason they can adapt to the new rules and powers there.
In this fanfiction, perhaps Sasuke could be a sort of anti - hero. He might initially be seen as a threat by the Demon Slayer corps because of his dark powers. But then, as the story progresses, he could use his Sharingan to detect demons more easily and work with the protagonists to defeat stronger demons.
There might be a fanfiction titled 'Naruto in the Demon Harem Realm'. In this story, Naruto could be transported to a realm where demon harems exist. He has to navigate this new world, deal with the different personalities of the demon girls in the harem, and perhaps use his ninja skills in unexpected ways. This could also lead to him growing as a character and learning more about the demon world and its ways.
Well, Tsunade could potentially be part of the harem. As the Hokage, she is used to power and might be interested in the unique power of the strong demon reader. Karin is another candidate. Given her own connection to unique powers in the Naruto world, she could be drawn to the demon reader. And lastly, Shizune. Her loyalty and kind nature might make her fall for the demon reader, thus making her a potential member of the harem.
Well, it could be about a female Naruto character who enters the world of Demon Slayer and Fairy Tail. Maybe she uses her ninja skills in the Demon Slayer universe to fight demons, and then somehow gets transported to the Fairy Tail world and teams up with the mages there. She could teach them some unique ninja techniques and in return learn some magic.
The fanfiction might also play with the idea of redemption for the female demon. Since the Doom Slayer is often associated with justice, perhaps he sees some potential in her to change. It could be a story of her trying to break free from her demonic nature with the help of the Doom Slayer. Their relationship could develop from pure enmity to something more complex, like an unlikely alliance or even a romantic connection in a more extreme take on the story.