Yang Xiao Long/History

She has a past with Ruby, who is presumably her adoptive younger sister and close friend. Ruby mentions that Yang used to read bedtime stories to her when they were young.

Junior's Club
Looking for information about a girl dressed in black, Yang heads to a night club and confronts a man at the bar named Junior. She attempts to coerce the information out of him, but he says he doesn't know. Yang is then surrounded by henchmen from the club and backs off. As she walks away from the bar with Junior she begins flirting and offers to give him a kiss, but punches him in the face instead. The henchmen then descend upon her and she beats them up. She comes under attack from the DJ above who is firing at her with a machine gun. After knocking him down to the club floor, two girls, Melanie and Miltiades, jump in to fight her. Despite some difficulty she manages to defeat each of the girls. By then, Junior recovers from Yang's punch and returns with a bazooka before firing several rockets at her. Yang manages to stop the rounds, but Junior then changes the bazooka into a bat and begins attacking her with it. She finally uses her shotgun gauntlets to destroy much of the club and knocks Junior out a window. Outside she runs into Ruby, who is confused to see her there.

Welcome to Beacon
Ruby Rose (episode)

Yang is first seen greeting Ruby Rose on the airship to Beacon Academy, displaying her excitement that her "little sis" will be attending the same school as her. She teases and then consoles Ruby when the latter displays her nervousness and even unhappiness that she might be treated as someone "special" at their new school.

The Shining Beacon

Yang shows concern for Ruby's apparent lack of social skills, and manages to create an opportunity to let Ruby learn on her own by dashing off with her friends, leaving Ruby alone (who falls down dizzy on Weiss Schnee's luggage).

The Shining Beacon, Pt.2

Yang reappears inside the auditorium of Beacon Academy where the students have gathered, and waves Ruby over beside her. She asks Ruby about her day so far, who responds by recounting the trouble she got into involving Weiss Schnee and Blake Belladonna. Yang at first thinks Ruby is joking, but realizes her little sister is telling the truth when Weiss comes up and starts berating Ruby again. She tries to play the easygoing mediator between the two, but with no success. Their heated conversation is interrupted when Professor Ozpin starts with his welcoming speech, and Yang shows some vague exasperation when Ozpin mentions that they are still nothing compared to the world they will enter. She mentions directly afterwards that Ozpin seemed "kind of off."

Later, when all the new students are preparing to go to sleep, Yang crashes next to Ruby and asks her about the letter she is writing. The two have a conversation where Ruby once again brings up her unhappiness at having to join the school without knowing anyone, but Yang tells her that there are plenty of friends at Beacon whom just hasn't met yet (after teasing her about Weiss being an enemy rather than a "negative friend"). Yang drags Ruby over to where Blake is reading a book, and attempts to engage the two  in a conversation. At first, Blake's aloof unsocialness causes the conversation to die multiple times and Ruby and Yang awkwardly try to pick it back up every time it happens, but after Yang proclaims that Blake is a "lost cause" Ruby inquires about the book Blake is reading, which starts what appears to be a genuine exchange between the two. However, Yang butts in and tells Ruby about how she is proud of her (for starting a conversation and expressing her dreams to be a protector of the peaceful world they live in so other people may enjoy it) and picks Ruby up, which annoys the latter and causes a brief fight between the two, until Weiss storms up and interrupts them again.

Beacon Academy Initiation
The First Step

Yang talks to Ruby while they are getting prepared for their initiation about what she will do about teams. When Ruby suggests that she would just join Yang's team, Yang insists her little sister should be more outgoing and find a team of her own. She and Ruby then talk to Jaune Arc who was put down coldly by Weiss, having had Pyrrha Nikos throw her spear at him. Yang remarks that he probably shouldn't have referred to Weiss as "Snow Angel" and the three of them then head to Beacon Cliffs for initiation. After Ozpin tells them about their initiation and how they will form teams, Yang is launched into the Emerald Forest with the other students.

The First Step, Pt.2

Yang is seen literally flying through the trees with a pair of aviators on, thoroughly enjoying the experience and extending it by using the kinetic energy from shots from her shotgun gauntlets to keep moving. After bouncing through the trees, Yang nails her landing and takes off. Shortly after when Ruby lands, she instantly starts looking for Yang in the hopes of making Yang her partner.

The Emerald Forest

While walking through the woods, Yang starts to become bored after not finding anyone. When she hears a rustle in the bushes, she wonders if it is Ruby, but is instead attacked by two Ursi. She dodges their attacks and almost seems to be playing with them, until she notices that a small strand of her hair was cut off. Yang goes into a rage at this and punches one of the Ursa with a flurry of punches, sending it flying into several trees. She goes to confront the other bear, but it is quickly killed by Blake Belladonna in a single strike. The two smile at each other and Yang claims that she could have taken him.

The Emerald Forest, Pt.2

Yang and Blake arrive at the Temple. As they approach it, they make note of that the relics are chess pieces and that some relics are missing, which suggests that they aren't the first to arrive. After Blake and Yang examine the chess pieces, Yang chooses a yellow knight because it looks like a "cute pony." When the two are about to leave the temple, they hear what sounds like a girl's scream. Yang asks Blake what they should do but she seems distracted by something above them; as Yang tries to get Blake's attention, Ruby suddenly falls from the sky.

Players and Pieces Yang is seen asking Blake on what they should do, which continues from the previous episode in reference to Jaune's girl scream. After seeing Ruby fall, she is left confused by the later turn of events, such as Nora riding on an Ursa, and when Pyrrha is running away from a Death Stalker, which chased her from from it's cave. Shortly after she tries to give her sister Ruby a hug, but is interrupted by Nora. When Ruby decides to attack the Deathstalker, she fails and is forced to run away. Yang rushes to her aid but is unable to after the Nevermore keeps them separate by a barrage of feathers. After Weiss saves Ruby, Yang hugs Ruby in delight knowing she is safe. Once Ruby and Jaune choose their chess pieces, Ruby leads both teams away as Yang smiles seeing that her sister is becoming what she knew she would. When Blake asks what is wrong, she implies it is nothing, but Blake seems to already know. Both teams are then split and each faces the Grimm species separately as JNPR faces the Death Stalker and RWBY faces the Nevermore. After a series of attacks prove unsuccessful, Ruby makes up a plan to beat the large bird. After helping Blake make a slingshot, which launches Ruby into the air with the help of of Weiss' seal. Yang watches in amazement as Ruby slays the Nevermore. She is later made an official member of Team RWBY, and hugs her sister in joy when Ruby is made leader.

Start of Class
The Badge and The Burden After rooming with her team, Yang wakes up with a joyful approach. She states that they need to decorate their room. She is seen placing a poster about a certain boy band named "The Achieve Men." When Ruby is suggesting they make bunk beds, Yang agrees along with Blake, while Weiss seems to be annoyed by the fact.

She later attends class, where she seems to have no interest, and seems to be wierded out by one of Professor Peter's gestures.

The Badge and The Burden, Pt.2

As Weiss faces down the released Boarbatusk, Yang cheers her teammate on along with Blake and Ruby. Later that night, she is seen asleep in her bunk bed above Blake.

Jaunedice

Yang is seen eating lunch with her team alongside Team JNPR, where she seems to be the only one interested interested in Nora's story. She later comments that it must be hard being a Faunus after seeing Cardin Winchester and his team teasing Velvet Scarlatina, a girl with rabbit ears.