Yes, there are quite a few. You can check some fanfiction websites like Fanfiction.net or Archive of Our Own. Just search for 'Harry Potter Ninjutsu' and you'll find a variety of stories that blend the magic of Harry Potter with the coolness of ninjutsu.
The plot could involve Naruto realizing the importance of medical ninjutsu after a major battle where many of his comrades are injured. He then seeks out a teacher, like Tsunade. He struggles at first with the precision required, but his willpower drives him to keep going.
In this type of fanfiction, the relationship between Harry and Snape can be re - imagined. Snape was Harry's teacher for Occlumency in the books, but often their interactions were tense. Fanfic writers may change this dynamic. They could have Snape be more patient or Harry be more receptive, which would lead to a different kind of mentorship and a new understanding between them.
One interesting lesson could be table manners in the wizarding world. There might be specific ways to hold a wand while dining or proper incantations to say before and after a meal. Another could be how to address different levels of wizards and witches, like the proper title for a powerful elder wizard. And perhaps the correct way to enter and exit a magical room or building, which could involve specific spells or gestures.
Well, a common theme is the training aspect. Imagine Harry Potter or his friends training in ninjutsu techniques under a strict sensei. It's also popular to have a theme of mystery, where the ninjutsu arts hold some secrets that are related to the wizarding world's past or future. And then there's the friendship theme, how the characters' relationships develop as they explore ninjutsu together.
It could be Dumbledore. He always has a knack for providing Harry with useful tools. Maybe he found this device during one of his travels and thought it would be beneficial for Harry's growth as a wizard.
Maybe a wizard who has traveled to far - off lands where voodoo is practiced could teach Harry. This wizard could have seen the power of voodoo and thought it could be useful in the fight against the Dark Arts in the wizarding world of Harry Potter.
Maybe Harry Potter uses a magical device to learn advanced spells. For example, he discovers a time - turning quill that allows him to study ancient magic more efficiently.
In 'Harry Potter Learns Voodoo' fanfiction, perhaps Harry would learn voodoo from a mysterious character who has some connection to the wizarding world. He could then combine voodoo spells with his own Hogwarts - taught magic. For example, using a voodoo charm to enhance his invisibility cloak's power. This would open up a whole new set of adventures and challenges for him as he tries to master this new form of magic while still dealing with the regular threats in the wizarding world.
Another reason is that it allows for a lot of creativity. Writers can create new mentors for Harry to learn from, new techniques of Legilimency, and new consequences of using it. It's a topic that can be combined with other elements of the Harry Potter world, like the prophecy, the Horcruxes, and the wizarding politics, creating a rich and engaging fanfiction.