A sense of curiosity is an excellent trait. It drives the OC to explore new ideas and experiment with different materials and chakra applications. Resourcefulness is also vital. Since they're an inventor in a ninja world, they may not always have access to modern - day materials. So, they need to be able to make do with what's available in the Naruto universe, like using special ninja plants to build parts for their inventions. Additionally, a bit of boldness helps. They should be brave enough to test their new inventions in dangerous situations, like in the middle of a battle.
Good OC traits for an inventor ninja in a Naruto fanfic could include being open - minded. This allows them to consider unconventional ideas and collaborate with other ninjas, even those from different clans. They should also have a strong work ethic. Inventing isn't easy, and they need to be willing to put in the time and effort. And having a bit of a rebellious streak can be interesting. Maybe they don't always follow the traditional ninja rules when it comes to their inventions. For instance, they might use a forbidden technique as part of their invention process, but for a good cause, like saving a village from a powerful enemy.