Effective character development involves giving each character a goal. The OC could have a goal of finding her true place in the ninja world. Madara's goal of uniting the clans and Izuna's goal of protecting his family will then interact with the OC's goal. Show how they conflict and align. Also, give them flaws. The OC might be too trusting at times. Madara could be overly ambitious to the point of being blind to some things. Izuna might be too deferential to Madara. By having these flaws, they become more relatable and the relationships more complex and interesting.
One idea could be a love triangle where the OC is caught between Madara's grand ambitions and Izuna's more personal loyalty. The OC might be a healer who tries to keep the peace between the two brothers while falling in love with both in different ways. For example, Madara's strength and leadership might attract the OC on one level, while Izuna's kind heart and protectiveness draw her in another way.
One more theme could be growth. Shiro, with her already high intelligence, and Izuna with her own abilities, can grow both individually and in their relationship. For instance, they could learn from each other's strengths and weaknesses. In some fanfictions, there might also be a theme of discovery, as they explore new aspects of the 'No Game No Life' world together, which is full of strange rules and entities.
Well, in fanfiction, the relationship between Hinata and Madara can be developed in many ways. Some might focus on a romantic relationship, where they overcome their differences. Others could explore a more platonic mentorship - like bond. For instance, Madara teaching Hinata some advanced ninja techniques, and in the process, they develop a deep respect for each other. This variety in relationship exploration is part of what makes Hinata and Madara fanfiction so appealing.
Another interesting point in Hinata and Madara fanfiction is the potential for character growth. Hinata could grow more confident in the presence of Madara, learning from his strength. Madara, on the other hand, might learn about the value of compassion from Hinata. Their relationship could be a catalyst for both of them to become better versions of themselves within the fan - created stories.
Well, in such a fanfiction, it might start with Naruto being in a situation where he becomes Madara's pet. Maybe at first, Naruto is defiant but as time passes, he could start to understand Madara's motives in some strange way. Madara, on the other hand, might initially see Naruto as just a possession but gradually develop a sense of attachment. It could be a really strange and complex relationship that unfolds as the story progresses.
Madara would have to adapt to the different threats in RWBY, mainly the Grimm. In his world, he was used to fighting other shinobi and clans. The Grimm are a whole new type of enemy. However, his Sharingan would give him an advantage in detecting their movements. He might also try to find a way to use the Grimm's negative energy, similar to how he used negative emotions in his own world to fuel his power.
Maybe an orphan from a non - Uchiha clan who has a special ability that Madara finds interesting. This character would be malleable and eager to learn from Madara, as they have no other real family or guidance. They could bring a fresh perspective to Madara's teachings.
One popular 'no game no life shiro x izuna fanfiction' might be found on fanfiction.net. You can search there using the relevant tags. Usually, the stories there range from cute and friendly interactions between Shiro and Izuna to more in - depth adventures where they team up.