It could be the elders of his clan. They are often the ones who make decisions in the clan, and if they see Naruto as a threat for whatever reason, they could be the main antagonists. They might be afraid of Naruto's growing power or his different way of thinking that could disrupt the traditional ways of the clan.
Well, one possible plot could be that Naruto is shunned by his clan due to some false accusations. Maybe they think he has some dark power within him that could endanger the clan. So, they cast him out, leaving him to fend for himself. This would lead to Naruto having to prove his worth on his own, without the support of his clan, and he might start to develop a more independent and self - reliant personality.
He could also try to find a new family or group to belong to. Maybe he befriends some outcasts in the village and forms a new kind of family with them. This new support system helps him cope by providing love and acceptance that he was denied by his own clan. He would learn that family isn't always about blood relations.
One possible reason could be fear. Naruto has the Nine - Tailed Fox sealed within him. His clan might have been afraid that this power could bring destruction upon them, so they chose to abandon him. Another reason could be a misunderstanding. Maybe they thought Naruto was somehow in league with the forces that brought the Nine - Tailed Fox to the village in the first place.
Fanfiction often takes creative liberties with Naruto clan kinjutsus. Writers may create new variations of existing kinjutsus or even invent entirely new ones. This can add an exciting element to the story, especially when these new kinjutsus are used in battles or to solve complex problems within the fan - created plot.
The Hyuga clan could also be a possibility. Given their strong bloodline and their focus on family and tradition, they might adopt Naruto. They could teach him their Gentle Fist technique. And Naruto could use his unique energy and determination to perhaps improve or modify the technique in some way. Plus, he could help the Hyuga clan with any external threats they face due to their valuable Byakugan.
Perhaps it could be a new character created specifically for the fanfiction. A young ninja from a minor clan who showed extraordinary talent in a unique form of jutsu. But because their clan was small and not very influential, and the larger clans felt threatened by this new talent, they managed to get the village to abandon this prodigy.
Another reason might be that they faced some sort of writer's block. Coming up with new plot ideas, especially for a crossover as complex as Naruto and Devil May Cry, can be really challenging. They might have hit a point where they didn't know how to progress the story further. Or perhaps they received some negative feedback early on that discouraged them from continuing.
One possible scenario in this fanfiction could be that Naruto grows up with the Namikaze Clan's unique jutsu training methods. He might inherit some of Minato's (a Namikaze) speed and intelligence in combat at a much earlier age. This could lead to him being a more confident and skilled ninja from the start, as the Namikaze Clan has a reputation for their strong abilities.
Adult - themed fanfiction often involves more mature interpretations of Naruto's clan kinjutsus. However, it's important to note that such content might not be suitable for all audiences. Some might explore the darker aspects of these kinjutsus, like how they could be misused in adult - like power struggles within the clans.