Yang Xiao Long, the Y of team RWBY, is the older half-sister of Ruby Rose. Born from their shared father, Taiyang Xiao Long and Yang's mother, Raven Branwen, Yang would not know Raven as her real mother initially, as Raven left the family behind for unknown purpose. Instead, Yang would see Summer Rose as her mother, despite Summer's frequent absence. , As big sisters do, Yang would often take care of Ruby in while Summer and Taiyang were away, even reading her bedtime stories.

When Summer passed away, Taiyang, in his heartbroken state, let slip that Yang's mother was actually Raven, who had disappeared when Yang was just a baby. Curious and driven to discover just who her mother was, Yang waited until Taiyang was away to follow a clue she'd found to her whereabouts. Ever the good sister, Yang packed Ruby in a wagon so she wouldn't be left alone and together the two wandered deep into the woods. Arriving at a cabin, the pair found not Raven but Beowolves that almost killed them, save the timely intervention of their uncle, Crow. From this moment on, Yang resolves to never let her search for Raven consumer her or endanger her loved ones again.

At age 17, Yang would attend Beacon Academy to become a huntress, falling in line with her strong sense of adventure and living carefree, along with Ruby, who had been given a special enrollment despite only being 15. It was at Beacon where she would meet Weiss Schnee and Blake Belladonna; the four being paired into team RWBY. The team would grow from partners to friends and learned much about the world of Remnant. Yang's straightforward, confident approach was difficult to miss and even harder to miss was her bright and sunny energy that fills a room. Still, Yang knew when to be serious, often taking a more mature role to care for her sister and team when needed, always being protective of them. Despite this, Yang had a temper that flared up whenever situations weren't going her way, costing her battles, nearly her life, and her right arm at the hands of Adam Taurus.

After the fall of beacon and the separation of team RWBY, Yang fell into a severe depression, suffering from PTSD-like symptoms at the mere drop of a dish. Nightmares haunted her often and Yang became reclusive, quiet, and lethargic. It took a lot of encouragement and advice from her father, Doctor Oobleck, and Professor Port to finally set Yang on the path to recovery. Through weeks of training with her father and a new robotic arm, Yang learned to balance her emotions; not forsaking her carefree attitude, but maintaining a level head and thinking decisions through. Coming out restored and with purpose again, Yang left the security of Patch, choosing to find her sister and burn bright once more.