He is the boyfriend of Mika Hayamura and an up-and-coming model who develops an obsession for working out in order to further his career. Yoma begins working out at Morioh Grand Hotel's gym where he eventually meets Rohan Kishibe, causing the two to become rivals in fitness.
Yoma is a young Japanese man of slightly above average height and an athletic build. He has short light hair with several dark spikes sticking out of it and side-swept bangs. A model scout considers him attractive enough to recruit, also stating that his face is quite small.
After beginning to train his body from his manager's suggestion, Yoma rapidly becomes very muscular. All of his muscles become defined, including his serratus anterior muscles which surprises Rohan. Over time, his shoulder and ankle muscles form into the shape of wings like those of the god Hermes.
As a model, Yoma wears several different outfits throughout the story. His first outfit consists of a vest on top of a hoodie along with casual pants and sneakers. While training, he either wears a sweatshirt, a t-shirt, or no shirt at all along with shorts. Sometimes he wears weightlifting gloves and wristbands. He also wears a string necklace with a pendant attached.
In the TV drama adaptation, Yoma keeps an unusual haircut consisting in a mix of standard haircut with unexplained small feathers sticking out of his hair. He first appears wearing a loose white hoodie with an "OSAFA" brand and loose grey pants. Under his hoodie, he wears a black tank top. After his muscles develop, Yoma challenges Rohan only wearing loose golden shorts with yellow leggings, and he's bandaged his hand and left arm with blue tape and black tape respectively.
After being hired as a model and working as an actor for a minor role in a movie, Yoma's confidence and dedication to improving his body progresses into egotistical self-obsession.
He follows a strict training regime, avoiding carbs and fats while only eating food containing protein. He decides that his diet would only contain steamed chicken, a heaping pile of egg whites, seaweed and mushroom salad, salmon with tomato sauce, Owson chicken salad, and a low-fat protein shake. He goes to sleep at 7 p.m., then wakes up at 4 a.m. and runs 10 kilometers.
Despite being in a cheerful mood while working out, Yoma becomes apathetic and rude toward others, lying and stealing for his own benefit as if everything was his own property. He becomes angry at minor infractions towards his strict training lifestyle and diet, not wanting to eat Walleye pollock roe spaghetti that his girlfriend Mika made and angrily yelling at a deliveryman who rang the doorbell three times at 7 p.m. He steals 5000 yen from Mika to buy protein and promises to pay her back but never does, and then eventually steals 270,000 yen from her debit card for his own personal training.
Yoma also starts taking over Mika's apartment, leaving his weights and training equipment all over the room, not caring that she trips over them. Acting as if the place belongs to him, he asks Mika if she can leave from her own home. He then manages to install a bouldering set all over the building for the sake of his training. His self-obsession drives him to murder Mika, his regular deliveryman, and a random stranger that took his personal trainer away from him, as they all disrupted his training regime in some way.
Yoma can also be competitive and vengeful in his determination to win. After building his body to an amazing extent, Yoma's initial loss against Rohan Kishibe in a treadmill match at the gym motivates him to turn their next competition into a life-or-death struggle in an effort to make it "fair" for his opponent.
Avatar of Hermes
As the avatar of Hermes, the god of athletic pursuits and exercise (among other things), Yoma Hashimoto is blessed with a supernaturally fit body, which allows him to become very muscled in a short amount of time.
He is capable of casually performing athletic feats such as running backwards at 20 km/h and throwing a 20 kg dumbbell with one hand while running, without breaking a sweat.
Yoma Hashimoto was once scouted by a model production agency because of his good looks. He managed to have photos of him published in a magazine, and had a minor role in a film. During the production, he could see the actors Takeru Satoh and Gō Ayano from a distance.
One day, his manager told him to work out, as good poses and exuding a certain aura were more important than sheer talent. Thus Yoma began to seriously develop his body by frequenting the Morioh Grand Hotel's gym on the 8th floor. Here, he met Rohan Kishibe, who became his acquaintance as well as a minor rival in a game. Said game was to run alongside each other on treadmills and try to take a small remote first once a certain running speed was reached.
Incidentally, Yoma's progress was remarkable, his trainer and girlfriend Mika remarking how quickly his muscles developed. However, he also developed a narcissistic streak and became obsessed with exercising. Living at Mika's apartment, he soon crowded her home with training equipment, but would also fight with her over his protein-rich diet and general obsession with fitness. Moreover, Yoma scolded a deliveryman who gave him protein for ringing the doorbell at 7 p.m., the time at which he wanted to sleep.
One day, Yoma's personal trainer was unavailable because of a client. Frustrated, Yoma stole 270,000 yen from Mika's credit card to subscribe to an expensive training program, covering her apartment and the building's facade with a bouldering set. At wit's end, Mika broke up with him and ordered him to leave. At an undisclosed time, Yoma murdered Mika, the deliveryman, and the other gym client, hiding their bodies encased in cement in various places. His muscles also kept developing at a tremendous speed, eventually taking the shape of wings at the trapezii, ankles, or other areas.
During one of his training sessions, Yoma met Rohan again. Despite a previous loss at their game, Yoma tried to ignore the mangaka until the latter teased him about his career. Upset, Yoma accepted Rohan's challenge. Exhibiting his exceptional body, causing Rohan to lose confidence, Yoma also threw a dumbbell at the window behind them, transforming the game into a life-or-death situation. Still sour about his previous loss, Yoma all but claimed that Rohan cheated and wanted a fair challenge, even breaking three of Rohan's fingers to prevent him from preemptively taking the remote. However, doing so allowed Rohan to partially transform Yoma's arm into a book and rapidly scribble a command.
At the critical moment, Yoma grabbed the remote first. Although he claimed victory, Rohan's command forced him to stop Rohan's treadmill, and Yoma was propelled backwards out of the building. Failing to grab the ledge, Yoma only menacingly muttered Rohan's name.
Although his ultimate fate is unknown, Rohan is sure that Yoma's athletic abilities enabled him to survive the fall or maybe stop his fall by clinging to the facade. He also reveals that Yoma is likely an avatar and is currently possessed by the God of Muscle, Hermes. Paranoid that Yoma would come back for him, Rohan decides to run.
- During the design stage of the OVA, Araki requested that Yoma be given a much stronger physique than what he had in the original one-shot.
- Kōki Uchiyama, who previously voiced Ikuro Hashizawa (Baoh) in All-Star Battle, voices Yoma Hashimoto in the OVA.