The main antagonist could also be a new character created specifically for the fanfic. This character could be an ancient evil that has been waiting for an opportunity to corrupt a powerful Huntress like Ruby. They would then use Ruby's newfound evil nature to further their own dark plans, and Weiss, Blake, and Yang would have to face both Ruby and this new threat.
Another possibility is that the antagonist could be Ruby herself in a sense. Her inner demons could be personified. As she turns evil, her own good side could be fighting against the darkness within her. So, her former self or the part of her that still has some goodness left could be the 'antagonist' as it tries to prevent the complete takeover of the evil Ruby.
If Ruby turns evil, she could become her own antagonist in a way. Her former self, the Ruby that was good, could be seen as what she is now fighting against. Her friends would also become antagonists as they try to stop her from causing more harm.
Perhaps it could be an evil version of one of Ruby's own relatives. Like an alternate version of her father or mother who has been corrupted by some dark force. They would then raise Ruby with their evil values, making her believe that what they do is right and leading her down a dark path.
It could be a powerful Grimm - like being that has evolved beyond the normal Grimm. This antagonist might have the ability to think and strategize like a human, making it a much more dangerous foe for Ruby and her team. It could be leading the Grimm attacks in a more organized way, targeting specific areas to cause maximum chaos.
One possible plot could be Ruby being betrayed by her closest friends. Maybe she discovers a dark secret about the Huntsman academies that makes her question everything she has ever believed in. This disillusionment could start her on the path to evil as she feels that the system she has dedicated her life to is corrupt.
It could be Salem. She has always been interested in the power of the silver eyes, and Ruby having those eyes makes her a prime target. Salem might send her minions to kidnap Ruby, which would lead to her disappearance.
Well, one possibility is that Ruby could be influenced by a powerful and evil relic. Maybe she discovers a dark side of the relic's power and becomes corrupted by it, gradually turning evil as she starts to value power over her friends and the greater good.
Well, her team members like Weiss, Blake, and Yang are likely to be important characters. Weiss could be trying to figure out what's wrong with Ruby and how to help her. Blake might use her own experiences with inner turmoil to try and relate to Ruby. And Yang would probably be very protective of her sister and be the first one to jump into action when Ruby is in trouble.
It could be Adam Taurus. He's a well - known and very radical member of the White Fang in the RWBY universe. His extreme views and violent methods would put him directly at odds with Ruby's more peaceful and inclusive approach.
One of the main themes is responsibility. As Ruby takes on the role of a queen, she has to be responsible for her actions and the well - being of those she leads. Courage is also there. She needs to be brave in the face of new challenges. Additionally, the theme of change is prominent as her new role changes her relationships and how she views herself and the world around her. It's about how she adapts to these changes.
One main theme is often adaptation. Ruby has to adapt to being mute, whether it's in combat or in her daily interactions. Another theme could be the importance of non - verbal communication. Since she can't speak, how she uses gestures, expressions etc. becomes crucial.