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.
Often, the resemblance could be in terms of the way Naruto stands or moves in these fanfictions. For example, Naruto might adopt a more menacing stance similar to Madara's. Also, his hair could be described in a way that it seems to mimic Madara's wild look, perhaps when he's in the middle of using a powerful jutsu.
In some fanfictions, it could be through a strange and powerful jutsu transfer. Maybe Madara, on the verge of defeat, decides to transfer his Rinnegan power to Naruto for some unforeseen reason, like seeing a new path for the ninja world in Naruto.
In this kind of fanfic, the author may describe Naruto's resemblance to Madara in terms of their auras. Naruto could have an aura that is as intimidating as Madara's. For example, when he enters a room, people might feel the same kind of pressure as they would when Madara was around. And perhaps Naruto starts to have some facial expressions that are similar to Madara's, like a certain smirk or a serious frown.
Well, in some fanfictions, Sage Madara might use his powerful chakra to create barriers around Sakura, restraining her physically. This could be a way to stop her from using her medical ninjutsu or combat skills against him.
Naruto might initially be on guard and hostile towards Edo Tensei Madara. But as Naruto is, he would also try to understand Madara's motives. He could start by trying to talk to Madara, asking him why he still clings to his old ways even in his undead state.
Fem Naruto's character development could also involve her learning from Madara's mistakes. Madara's past actions led to a lot of destruction. Fem Naruto, seeing this, could vow to take a different path. This would require her to grow in wisdom and restraint. On the other hand, Madara could develop by seeing Fem Naruto's potential. He might start to believe in a better future for the ninja world through her, which would be a huge shift in his character from his more nihilistic views in the original story.
For Hashirama, emphasize his idealistic side. He is always looking for ways to bring about peace, so in the fanfiction, he could be constantly proposing new ideas to Madara. His character should also be shown as kind - hearted. For instance, if they encounter a wounded animal or person, Hashirama would be the first to offer help. Madara, on the other hand, is complex. He has a dark past and a sense of ambition. Write about his internal struggles, like his conflict between his loyalty to his clan and his own desires. When they are together, their conversations should be full of tension and a sense of history, as they have a long - standing relationship filled with both friendship and rivalry.
To write a madara x original character fanfiction, start with understanding Madara's character. He's a complex figure with a lot of history. Your original character could be someone who challenges his beliefs or complements them. For instance, if your character is from a different clan with unique abilities, how would that play into their relationship? Make sure to have a good flow in your writing, and use dialogue to show their chemistry.