She was never potty trained

Ruby Rose always stood out among a crowd for many reasons. She was well-known for her unique silver eyes, her expertise in designing weapons, and the smell that came from her whenever she needed a new diaper.

Despite being almost nineteen years old, Ruby was still in diapers, and didn't even know how to use the potty. When she was starting to learn how to use the potty, her mother, Summer Rose, had tragically passed away, and thanks to a combination of a traumatic experience when she was out looking for her mother with her sister Yang, and their father being too consumed with grief, there was never really a good time to start potty training her again, not that she minded it. While she was aware of the looks she got at times, Ruby was never really that bothered by her need for diapers, and even enjoyed the comfort and convenience they brought.

Because she didn't have to worry about potty breaks, Ruby dedicated far more time to her studies, working on customizing her weapon, and combat training. She was so skilled, she managed to stop a robbery on her own, which attracted the attention of the headmaster of the prestigious Beacon Academy, Professor Ozpin. He was so impressed by her performance, he gave her a scholarship to Beacon two years before she could even apply, meaning she could go to the same school as Yang. After a lot of packing, Ruby and Yang boarded the airship that would take them to Beacon Academy.

"I still can't believe my baby sister is going to Beacon with me! It feels like yesterday that you were still in diapers." Yang said happily.

Ruby giggled at the joke, despite how often Yang made it. "That WAS yesterday, Yang." She said, making the same response to Yang's comment that she always made.

After the airship landed, Ruby and Yang went their separate ways as Yang went off to spend time with her other friends, leaving Ruby alone in Beacon's courtyard