In the picture found by Osamu, Mato appeared to be a young woman with dark-coloured twin-tail hair that rested over both of her shoulders. She is also seen wearing a light-coloured long-sleeved t-shirt and a dark-coloured pants.
Not much is known about her personality.
At a certain point of time before the start of the series, she joined an organization now known as Old Border. It is unknown whether she participated in the mission around five years ago which killed ten of her friends. Sometime after the incident, she decided to leave and resume civilian life.