One plotline could be that Penny is hacked by an enemy and turned into a brainwasher to manipulate her friends in RWBY. This would create a lot of internal conflict as the team tries to figure out what has happened to her.
Perhaps Penny is forced to brainwash others as part of a secret experiment gone wrong. And she has to struggle against her programming while her friends try to rescue her and reverse the brainwashing effects on those she has already affected.
It could also be that an outside force uses Penny's innocent and helpful nature against her, making her believe that brainwashing people is for their own good. This would lead to a complex moral dilemma for the RWBY characters as they deal with a well - intentioned but mis - guided Penny.
One possible place to start looking for such fanfiction is Archive of Our Own (AO3). There are often a variety of unique takes on RWBY characters in fan-created works there.
One possible theme could be self - discovery. As the character is reincarnated as Penny, they have to figure out who they are in this new form. Another theme might be friendship, as they interact with the other characters in the RWBY world as Penny. Also, the theme of adaptation, since they need to adapt to Penny's abilities and the situation she is in.
Another plotline might be that Jaune is framed for a crime he didn't commit and decides to disappear to clear his name. He goes into hiding and starts his own investigation, all while his friends in RWBY are trying to figure out what really happened and whether he's actually guilty or not.
Perhaps a plotline where the values that Mao Zedong represented, like equality and the fight for the common good, are transferred to the RWBY universe. The RWBY characters could be inspired to fight not just for themselves but for all the people in the kingdoms. They could start new initiatives like ensuring equal access to training for all those who want to be huntsmen or huntresses, similar to how Mao Zedong fought for the rights of the common people in China.
Maybe a plot where Glynda's telepathy is somehow affected by an outside force. This could lead to her losing control over it at times and causing chaos, and she has to find a way to regain control and fix the problems it causes. It could also involve her learning more about her own power through this struggle.
Well, it could involve the RWBY characters seeing future versions of themselves. Maybe they see how their relationships have evolved or how their combat skills have improved. They might also witness future threats to Remnant and start preparing for them in the present.
Well, a possible plotline could start with Ruby being somehow infected or cursed to become a Grimm. She would then experience a whole new set of emotions and abilities. Maybe she starts to have visions or dreams related to the Grimm's origin or their purpose. As she tries to understand what has happened to her, she might be ostracized by some of her friends who are afraid of her new form. However, a few might believe in her and help her. She could then try to use her new Grimm - like abilities, such as enhanced strength or stealth, to fight against a greater evil that is threatening both the Grimm and the people of Remnant. Along the way, she could learn more about the true nature of the Grimm and find a way to either reverse her condition or fully embrace it in a way that benefits everyone.
One possible plotline could be that Ruby discovers her hidden princess heritage and has to balance her normal Huntsman duties with the newfound responsibilities of royalty. Maybe she has to attend grand balls and diplomatic meetings while still trying to fight Grimm. Another could be that she has a secret princess identity that she uses to infiltrate an enemy kingdom or group, using her charm and skills as Ruby as well as her new royal persona.
One possible plotline could be that Cinder starts off secretly admiring Pyrrha's combat skills. Maybe she spies on Pyrrha's training sessions and tries to learn from her techniques. This could lead to a situation where Cinder has an internal struggle between her admiration for Pyrrha and her own dark motives in the main RWBY storyline.
Another plotline could involve Adam's relationships at Beacon. He might form an unexpected friendship with a human student who challenges his pre - existing beliefs about humans. This friendship could be a central part of his character development in the fanfiction, as he starts to question his long - held grudges and biases.