- “No one hustles Yama!”
- ―Yama to Hiro
In earlier drafts, Yama was intended to be a more important antagonist as a mob boss in San Fransokyo's crime scene. He was the sumo wrestler leader of a gang that worked for Yokai, which consisted of rocket-powered bomber men, and the Fujitas; a group of martial artist roller women in traditional Japanese wear and makeup. Some concept art for Yama depicted him with full body Yakuza style tattoos or donning masks similar to those found in certain Japanese wrestling circles. 
Yama is a local crime boss living in the city of San Fransokyo. He has partaken in various illegal acts such as bot fighting, thievery, illegal money lending and murder. With his gruff and powerful demeanor (coupled by his massive physique) Yama has gained a notorious reputation, and is amongst the most feared members of San Fransokyo's underworld. His base of operation is in a shady district known as "Good Luck Alley", which is heavily guarded by a slew of subordinates under Yama's authority.
Yama is first introduced as the undisputed bot-fighter champion in San Fransokyo's underground bot fights with his prize robot, Little Yama. After defeating an unfortunate contender, a boy named Hiro Hamada shows up and asks if he can participate with his own robot. Yama, underwhelmed by Hiro's naive demeanor, agrees to fight the boy. When Hiro's bot seems to collapse after the first round, Yama is about to gloat in his victory until Hiro bribes him with more money for a rematch. The confident Yama accepts this and the match restarts.
However, Hiro's bot is revealed to be highly advanced, quickly repairing itself and destroying Little Yama with ease. Hiro brazenly boasts about his victory until Yama, out of spite, has his goons attack the boy and chase him into the alley. When the group seems to have Hiro cornered, Hiro's brother Tadashi rescues him on his moped away from the goons.
The brothers, along with Yama's gang and everyone in the bot fights, are caught and arrested by the San Fransokyo police during the escape. Yama and his gang are forced to share a cramped cell with Tadashi, while Hiro has a separate cell to himself due to being a minor. Hiro and Tadashi are released that same night on account of their aunt, while Yama and his henchmen are presumably left in the police station. He isn't shown for the rest of the film after this.
Not long after his and his gang's arrest, Yama was released and returned to his criminal activity, appearing to be working for an unseen man that goes by "Obake".
When Yama and his men were holding a man by his feet as they threatened to drop him if he didn't give them money, Yama received a call from Obake, along with the task of retrieving a sculpture from San Fransokyo Institute of Technology. As Yama was coming up with ways to get it, he and his men come across an out-of-control, wandering robot, along with Hiro. Vengeful, Yama decided to use this opportunity to give Hiro the "lesson" that they weren't able to give him at the bot fights.
However, when they were in the middle of hanging Hiro by the feet to drop him on the side of the building, Yama saw Hiro's ID for SFIT and realized that he is a student and could serve as their "little helper" in obtaining the sculpture. To make sure that Hiro does as they say, Yama held the robot they obtained from him as a bargaining chip; the sculpture for the robot. In truth, Yama has no interest in giving it back, which was proven when Hiro and his friend gave Yama what he asked for but still planned to give Hiro his "lesson" of the night and keep the robot for himself. After three superheroes infiltrated and save the two from them and take the robot back, Yama has already made copies of it in the form of a powerful army that would obey his commands.
Yama's employer wasn't happy when he learned that he lost the sculpture and uses his hacking to make the elevator that Yama was in plummet from a high level; fortunately Obake was pleased with the robotic army that Yama built and how he planned to use them to get the sculpture back. As Yama's new robots attacked the city as a distraction, he and a small number of Baymaxes went to SFIT to obtain the sculpture himself; with no knowledge that "Zero" and his robot were also at the school. Yama was having trouble finding the room that it was kept in and the item itself until he hurt himself and one of his robot minions revealed itself to be an imposter, with the sculpture in its hand.
After a piece of the sculpture breaks off and revealed a powerful energy source that overcharges anything electronic from the inside of it, Yama called Obake to ask him why he didn't warn him about the dangers of it; in which his boss replies by telling Yama that a "dog" doesn't need to know or ask what it is fetching for its master. With Yama escaping from the group of superheroes with the entity in his pocket, it melts itself through his clothing and out of the pocket as it attaches itself to a train and makes it go out of control; and far out of Yama's reach. Yama is left empty handed as the damaged sculpture is later destroyed.
In "Food Fight", Yama hires a skilled thief, Momakase, to steal a prototype gravitational disruptor from Alistair Krei. Once she had got it, Momakase decided to keep it for herself and poisons Yama with sushi that made him ill.
Yama is the main antagonist of the video game, Battle in the Bay, where he sought revenge against Hiro for defeating him in the bot-fighting tournament. To do so, Yama invaded San Fransokyo with an army of battle bots, setting them against the Big Hero 6 team. After a battle on the Golden Gate Bridge, however, Yama is defeated and sent back to prison.
Yama served as a minor antagonist, serving as the primary enemy in the first stage of the game where he, once again, made an attempt to avenge his own defeat by terminating Hiro.
- "Yama" is Japanese for "mountain."