Masu-san bears the basic appearance of Leiji Matsumoto's characters, a mostly ovaloid-looking body. She has gray hair with a bun tied behind the back of her head. Masu-san's small, circular glasses are located near her mouth. She is almost always seen dressed in a shirt, vest, skirt, apron, and shoes.
Masu-san is a cheerful elderly woman who enjoys the company she receives on the Arcadia. She is also very dedicated to her cooking, becoming surprisingly violent if anyone tries to steal her ingredients, usually Bird or Me-kun, brandishing her kitchen knives to attack them. Masu-san has known Dr. Zero for a long time and the anime reveals a history of helping him with the Tokaga people.