In the fanfiction, a possible plot could be that Si - as Ruby - discovers some long - hidden secrets about Ruby's family or the history of Remnant. This discovery could lead to a whole new set of adventures and challenges. For example, they might find a connection between Ruby's family and an ancient power that could change the fate of Remnant.
I'm not sure specifically as there could be many different versions of such a fanfiction. But generally, it might involve the character Si being reborn as Ruby and then facing all the challenges and adventures within the RWBY universe. Maybe they would have to deal with Grimm, make new friends like Weiss, Blake and Yang, and also attend Beacon Academy.
Most likely Weiss, Blake and Yang. They are Ruby's teammates in RWBY and would play important roles in any fanfiction where Si is reborn as Ruby. They would be there to support and fight alongside the reborn Ruby (Si).
Well, Weiss could be one of the main characters. She might initially be skeptical of this 'new' Ruby but then grows to accept and rely on her. Their relationship could be full of bickering at first but then develop into a strong friendship.
Some fanfictions might have a plot where Ruby's blindness is a temporary state caused by some dark magic or a powerful enemy's attack. During this time, she has to quickly learn to function without her sight. Her friends, like Weiss, Blake, and Yang, would be by her side, each using their own skills to support her. Weiss could use her glyphs to create paths or barriers that Ruby can sense, Blake could use her stealth to scout ahead and warn Ruby of any danger, and Yang could be her physical protector, ready to fight off any threats that come their way.
One possible plot could be Ruby trying to prove her innocence. Maybe she was framed for something she didn't do. For example, a powerful relic goes missing and Ruby is wrongly accused. She then has to embark on a journey outside of the school to find the real culprit and clear her name.
One interesting plot could be Ruby sleepwalking into a mysterious area of Beacon Academy that she's never seen before. Maybe it's an old, forgotten part filled with secrets. Another plot could involve her sleepwalking during a Grimm attack and somehow unconsciously using her powers in a unique way to fend them off. For example, her scythe might move on its own to block attacks while she's asleep.
One interesting plot could be Ruby and Mercury teaming up against a common enemy. Maybe a new Grimm type that they have to figure out how to defeat together. Their different fighting styles, Ruby's speed and scythe - wielding skills combined with Mercury's acrobatic and martial - arts - based combat could make for some exciting action scenes.
One possible plot could be Ruby Rose trying to understand Salem's motives. Maybe Ruby, with her pure heart, believes there's a chance to redeem Salem. She could engage in a series of intense conversations with Salem, where Ruby tries to appeal to any good that might still be in her. This would be a great exploration of the themes of good versus evil and redemption.
If Si was reborn as Ruby's twin, it could change the whole dynamic of the story. For example, they could share a special connection to the silver - eyed power. Maybe the twin would have a different take on how to use it or discover new aspects of it. This could lead to new story arcs where they have to figure out how to control and utilize this power together. Also, in the Beacon Academy days, they could be a duo that everyone looks up to, inspiring other students with their teamwork and twin synergy.
In this fanfiction, an exciting plot could be Si being reborn as Finn but with some of his own memories intact. He then tries to find a way to merge his old self with Finn's heroic identity. Along the way, he might meet Jake and they could go on adventures together. Si could also have to deal with the moral dilemmas that Finn sometimes faces, like whether to help a villain who seems to have a good side.