An OC with a strong and independent personality would be great. For example, an OC who is a skilled ninja in her own right, like a master of stealth or a powerful genjutsu user. This way, she can match Genma's abilities and they can have an equal partnership.
Naruto might initially be a bit jealous that Genma is spending so much time teaching Sakura. But as he sees Sakura improve, he starts to respect the process. Genma, on the other hand, might see Naruto's potential through his connection with Sakura and start to offer some indirect advice to Naruto as well. Sakura would grow to have a new level of respect for Genma as her teacher.
The theme of sacrifice often appears. Genma might be in a situation where he has to sacrifice something for the greater good of Konoha or his friends. Also, the exploration of Genma's place in the ninja hierarchy is a theme. How he fits in among the other powerful shinobi in the village is something fanfictions like to play with.
One common theme is loyalty. Genma is often shown to be extremely loyal to the Hidden Leaf village in fanfics. Another theme is friendship, as he forms bonds with other characters. For example, his relationship with his comrades in Team Ro is often explored.
Some interesting 'Naruto Genma' fanfics include 'Genma's Secret Mission'. In this fanfic, Genma is sent on a top - secret mission that could change the fate of the Hidden Leaf Village. 'Genma and the Mysterious Stranger' is another one where Genma encounters a strange figure that leads him on a journey full of mystery and danger. There's also 'Genma's Redemption' which focuses on Genma's path to redeem himself after making a big mistake in the past.
One interesting storyline could be Genma as a mentor to a young ninja. He could pass on his unique skills and knowledge. For example, his kenjutsu skills can be taught to a new generation, adding a new dimension to the story.
You can start by looking on fanfiction.net. It has a large collection of Naruto - related fanfics, and there are bound to be some good 'Naruto Genma' ones there. Another option is Archive of Our Own (AO3). It also has a wide range of fan - created content, including fanfics about Genma from Naruto.
Sure. 'Genma's New Mission' is quite interesting. It focuses on Genma getting a unique and challenging mission that tests his skills in new ways. Another one is 'Genma and the Hidden Power' which delves into Genma discovering a hidden power within himself.
One great Genma Naruto fanfic is 'Genma's Hidden Path'. It delves into Genma's character in a way that the original series didn't fully explore. It shows his backstory and his relationships within the Hidden Leaf village. Another is 'Genma's Missions Unveiled' which focuses on his various dangerous missions and how he overcomes challenges.