There could be new antagonists created specifically for this fanfic. Maybe some dark forces that were sealed away by Asura long ago are awakened. They would oppose Naruto because they see him as a threat to their resurrection or their evil plans.
The fanfic could involve Asura taking Naruto to some secret places for training. There, Naruto might discover hidden aspects of his own heritage. He could also meet other powerful beings related to Asura. Asura could train Naruto to master his emotions better, which is crucial in the ninja world. This training would help Naruto make more rational decisions during high - stress situations like in the middle of a war or when facing a powerful enemy who tries to manipulate his feelings.
One way to blend the worlds is through the concept of power. Asura Wrath has incredibly powerful and god - like beings. In a fanfic, you could have Naruto characters encounter these powerful entities. For example, Naruto himself could meet Asura and learn about a different kind of chakra or power source. This would not only introduce a new element to the Naruto world but also create an interesting dynamic as Naruto's ideology of never giving up might be put to the test against the seemingly invincible Asura.
Kosuke might be a character created specifically for this fanfic. He could be someone with a unique background, like perhaps he was once a disciple of a great ninja but then went on his own path. And now he sees potential in Naruto and decides to train him. He could have abilities that are different from the main characters in the original Naruto series, which is why he has something new to offer to Naruto in terms of training.
In this fanfic, Lilith could be an original character created by the author. She might be a powerful and mysterious figure with special abilities that make her suitable to train Naruto.
She could be someone with a special bloodline or ability. Maybe she has a unique form of chakra that gives her certain powers. In the context of training Naruto, her skills and knowledge are what make her important. She could be a mysterious figure who has been observing Naruto for a while and decides to take him under her wing to help him reach his full potential. For instance, she might have the ability to see the latent potential in others and wants to shape Naruto into a great ninja not just for his own sake, but also for the greater good of the ninja world.
It could lead to Naruto becoming even stronger and more skilled than in the original story. Jiraiya's training methods might unlock new powers for him.
Dark Naruto in such fanfic is often portrayed as more brooding and intense. He may have a more cynical view of the world compared to the regular Naruto. His appearance might also be different, with darker clothing or a more menacing look.
Another great one might be the fanfic that focuses on a crossover of Naruto's ninja world and DxD's supernatural world from the perspective of a character who has Asura's essence. It has some really cool fight scenes where Naruto - style jutsus are pitted against DxD's magic and special abilities.