One idea could be that Ruby Rose's little brother discovers he has a unique power that no one in the family expected. For example, he might be able to manipulate time in small ways, like slowing it down during a battle to gain an advantage.
One plot idea could be that Naruto finds himself in the world of Ruby Rose. He might use his ninja skills to help Ruby and her team in their battles against Grimm. For example, his shadow clone jutsu could be used to create distractions while Ruby attacks. Another idea is that they meet during a cross - dimensional event and have to learn about each other's powers and cultures to find a way back to their respective worlds.
Maybe a plot where Ruby discovers a hidden part of her family's past that links her to the Scarlet Spider in some way. This could lead to her having to learn new abilities or face a moral dilemma as she gets involved with the Scarlet Spider's more gritty and morally ambiguous world compared to the more straightforward good - vs - evil of RWBY.
Well, in some fanfictions, a male Ruby might be from a different background than the original Ruby. This could lead to an interesting dynamic with Weiss. For example, he could be from a more noble family, which causes some initial friction with Weiss, who is also from a noble background. As they work through their differences, a White Rose relationship begins to develop. It could involve them facing off against a new type of Grimm that only male Ruby's special skills can help defeat, bringing them closer together.
To develop his character, consider his backstory. Maybe he had a tough time growing up because people always compared him to Ruby. This could have made him determined to be different. Also, think about how he interacts with other characters in the fanfiction world. If there are villains, does he try to reason with them first or jump straight into fighting? His actions will show his character. For example, if he's a compassionate person, he might try to understand the motives of the villains and help them reform if possible.
A third plot idea is that they participate in a tournament together. They have to compete against other teams from different academies. During the tournament, they face some tough opponents who target their weaknesses. Ruby and Blake have to train hard together to overcome these challenges. In the process, they learn new techniques from each other and their relationship evolves from just being teammates to being really close friends who trust each other completely.
One idea could be Ruby adjusting to her new cyborg body and the enhanced abilities it gives her, like super - strength or advanced weaponry integration. Another could be her facing discrimination from some in the RWBY world who fear or mistrust cyborgs.
A more complex plot could be that there is a prophecy in both worlds about a union between someone from the Naruto universe and someone from Ruby's universe. Naruto and Ruby are the ones fated to fulfill this prophecy. They initially don't get along but as they face various challenges together, they start to understand each other and fall in love, while also saving both their worlds in the process.
One plot idea could be Ruby discovering she has werewolf abilities during a mission. She has to learn to control it while still fighting Grimm. Another could be that in a werewolf form, Ruby has enhanced senses that help her track down a powerful and elusive enemy. Or perhaps she forms a pack with some of her friends who also get werewolf-like powers and they have to protect Vale from a new werewolf - Grimm hybrid threat.
One idea could be Ruby discovering she has some cheetah - like abilities. Maybe she's faster than ever and has to learn how to control this new power. It could add an interesting dynamic to her combat style and how she interacts with her team.
Another plot could involve their friends' reactions. Yang could be overprotective, while Blake might offer more calm and practical advice. The story could focus on how their relationships with their friends change as they prepare for the babies. They might also have to deal with the expectations of their families.