Masaru has light purple wrinkled skin; dark purple, shoulder-length hair with the fringes swept to the right; and an overweight body. Like Takashi, he wears a hospital gown when inside the Nursery. Due to childhood polio, Masaru is often seen a specialized floating wheelchair that comes with a protective glass covering.
During the beginning of the movie when Masaru went with Colonel Shikishima to retrieve Takashi, Masarue wore a green suit with a double-breasted jacket, a deep purple tie, a red dress shirt, dark brown dress shoes, and a deep purple handkerchief in his chest pocket.
In the Espers' flashback, Masaru had neatly combed short black hair, and he wore a white collared shirt with brown shorts, shoes, and white socks. His hair was as short as Takashi's, and he was slightly skinnier. He also looked his actual age, since the flashback took place sometime before the government's psychic experiments began.
Despite having the body of a child, he has premature aging which makes him appear between his late 40's and early 50's.
In contrast to his friend Takashi, Masaru is braver and more mature. He will quickly attack anything he deems a threat to himself and/or his friends, but he is also reasonable and caring. He often takes charge of the group, which seemingly makes him the leader of the Espers, but in reality his friend Kiyoko has the final say in the Espers' decisions.
While he is considered wise beyond his age, Masaru's mindset is still akin to a young child and because of the isolated lifestyle he lives in, he is ignorant of many things. For example, he is terrified by the sight of blood to the point of running away. However, it is implied, with his past discovery of Akira, that he had some idea of what the government had in mind for psychic children like him.
Masaru is very close friends with the Espers, but out of all of them he is closest to Kiyoko, who is constantly bedridden. Because of the girl's physical fraility, Masaru is very protective of her and her safety is put above all else.
Masaru was one of a large group of young children who were taken in by the government of the original Tokyo to participate in a secret parapsychology project that studied the development of psychic powers, presumably for military or political reasons. Since no mention was made of his parents, it was implied that Masaru was an orphan who became a ward of the state.
One day, Masaru wandered off by himself and came across a room where he found a boy named Akira lying on an operating table, hooked up to various machines. Shortly after this discovery, Masaru was subjected to a series of horrendous experiments and tests that forced him to develop psychic powers. He also was affected with childhood polio as the result of the experiments, rendering him unable to walk again.
During his time as a psychic test subject, Masaru befriended Akira, as well as Kiyoko and Takashi who were also orphans. Out of all the children taken in by the government, Masaru and his three friends were the only ones who survived the government's testing long enough to gain strong psychic abilities. Akira's powers later grew beyond the government's control, which resulted in the accidental creation of a psychic explosion that utterly obliterated Tokyo.
To hide information about the project, as well as prevent another psychic explosion from happening, Masaru, Kiyoko, and Takashi were put in prolonged isolation, kept on the routine feeding of drugs that suppressed their psychic powers. This eventually led to premature aging and the development of physical handicaps. While his friend Takashi remained physically healthy for the most part, Kiyoko wasn't as lucky; she became so weak she was permanently bedridden, relying on medicine and life support systems to stay alive.
After Takashi was taken from the Nursery by anti-government resistance members who mistook the boy for Akira, Masaru helped the Colonel locate him by using his clairvoyance to pinpoint Takashi's location. He eventually found Takashi in the Route 5 highway and, despite Takashi's reluctance to return to the Nursery, convinces his friend to come back.
Shortly after Tetsuo Shima, a young Capsule gang member, is taken in by the government to become a psychic test subject, Masaru teams up with Takashi and Kiyoko to psychically assassinate Tetsuo, fearing his great power and wanting to protect Neo-Tokyo from destruction. Using the Nursery's toys to disguise themselves as a toy car, a bear, and a rabbit respectively, they invade Tetsuo's hospital room with the intent to kill. While trying to defend himself from the Espers, Tetsuo accidentally steps on a glass cup and cuts himself in the foot, shedding blood. The Espers, terrified at the sight of Tetsuo's blood, are forced to retreat, revealing themselves to Tetsuo in the process.
Masaru's main ability is psychokinesis. While not as powerful as the likes of Tetsuo and Akira, Masaru is very skilled in using it in a variety of ways. He can take on the form of a giant toy car by psychically covering himself with children's toys like a full-body exoskeleton, and when combined with Takashi's abilties, Masaru can fight almost on par with Tetsuo.
Masaru possesses a form of clairvoyance that allows him to pinpoint the location of other psychics. This power is shared with his manga incarnation. He also has telepathic powers and can mentally communicate with other people like the Espers.