Masashi Yamada is a minor character in Gantz, introduced as an elementary school teacher who is pulled into the deadly game organized by the mysterious black sphere. He teaches first graders at Nerima Elementary School and is a man of average height and build, with tidy black hair and large glasses, typically dressed in formal attire such as a dark suit, white shirt, and tie due to his profession.

His background is that of an ordinary civilian; prior to his involvement with Gantz, he died in a bicycle accident and was subsequently transported to the Gantz room along with other recently deceased individuals. As a result, he becomes a member of the Tokyo Team, but his participation is extremely brief. He appears only during a single mission, known as the Onion Alien or Cebola Alien mission, and lacks any notable combat experience or special abilities. Like most newcomers, he is initially confused and frightened by the situation.

Personality-wise, little is revealed about his inner motivations or character traits due to his short time in the story. He appears to be a mild-mannered and ordinary person, reacting with understandable fear and uncertainty when confronted with the violent and surreal nature of the Gantz missions. He does not form any significant relationships with the main cast, nor does he undergo any character development, as he is killed during his first and only mission. His death occurs relatively early, serving as a reminder of the high stakes and the grim fate that awaits many unprepared participants. Masashi Yamada thus functions as a tragic, expendable figure whose ordinary life is abruptly ended by the brutal game.