One possibility could be that Naruto discovers a hidden ability within himself to use Wood - Style Treant Jutsu. Maybe he unlocks it during a life - threatening battle where he needs to protect his friends. He could combine his own chakra with some ancient energy source in the forest to create these powerful treant - like creatures that fight on his side.
The fanfic could start with Naruto having a strange dream about using Wood - Style Treant Jutsu. He wakes up curious and starts to experiment. He finds that he can transfer his own emotions into the treants, making them more aggressive or defensive depending on how he feels. As he gets better at it, he uses the jutsu in a major battle against a group of rogue ninjas who are terrorizing a village. His treants become a symbol of hope for the villagers as they fight off the invaders.
The Treant could have the ability to absorb and store chakra from the environment. Just like real trees absorb sunlight and nutrients, this Treant made by Naruto could soak up ambient chakra, making it stronger over time. It could also use its branches to perform long - range attacks, similar to how a ninja would use kunai or shuriken. And, it might be able to camouflage itself as a normal tree in the forest, giving Naruto an element of surprise in battle.
Well, in the Naruto universe, for Naruto to make a Treant Jutsu, he might first need to study nature chakra deeply. He could observe how trees grow and thrive, and then try to infuse his own chakra with the essence of nature. Maybe he'd have to combine his shadow clone jutsu in a new way, having clones study different aspects of trees, like their root systems and how they absorb nutrients. Then he could use his Rasengan as a base and add the nature - based tree - like elements to it, gradually forming a Treant - like structure out of his chakra.
Sure. In fanfiction, the rules can be bent or rewritten. Maybe Naruto discovers a hidden bloodline connection that enables him to use Wood Style. It could be that he has a distant relation to the Senju clan that was previously unknown. This new ability would change the dynamics in battles and his relationships with other characters like Sasuke and Sakura, as he would have a whole new set of skills to bring to the table.
The combination of two very different universes, Naruto and DxD, makes it interesting. The Reverse Harem Jutsu from Naruto is a fun element to introduce into the DxD world. It can lead to some really unique and unexpected interactions between the characters from both series.
One way could be through a special training with a character who already has Wood Style or knowledge of it. For instance, if Yamato decided to train Naruto intensively in Wood Style techniques.
One idea could be a fanfic where a young ninja discovers a unique way to combine lightning jutsu with other elements like water, creating a new and powerful technique. This could lead to him being sought after by different clans for his knowledge.
Maybe Sasuke. Although they are rivals, they also have a deep bond. Sasuke might have come across a unique jutsu during his travels and decide to teach it to Naruto so that they can both become stronger and better protect their village.
He could practice in secret locations where no one can see him. For example, in an abandoned cave or a hidden part of the forest. That way, no one will know about the new jutsu he's developing.