Sgt. Major Melissa Mao is one of the main protagonists of the light novel and anime series Full Metal Panic!. She is a 25-year-old former marine and SRT's second-in-command in Mithril. Her subordinates include Sousuke Sagara and Kurz Weber. Her expertise in electronic warfare is valued by the Pacific Battle Group Tuatha de Danaan.
She is voiced by Michiko Neya in the Japanese version of the anime and Allison Keith in the English version, the former of whom also voices Princess Natalia.
Melissa is a tall woman with violet eyes and short purple hair. She has fairly large breasts and a flawless skin complexion. When not on duty, she is usually seen wearing some combination of a shirt and trousers.
Melissa is a very tomboyish woman, acting considerably less feminine than either Tessa or Kaname. She is an extremely heavy smoker and even heavier drinker, once having many cigarettes and a minimum of 20 beer cans sprawled out on Tessa's coffee table, much to her disgust. She is extremely rude, preferring to use heavy language when talking to someone angering her or someone she can not stand.
In the Fumoffu episode The Warcry of Excessiveness, Sousuke is shown using extremely heavy language based on the training Melissa gave him. She also enjoys a practical joke or two. Once in the series when Sousuke called to protest Tessa's staying in his apartment, she gave him permission to "jump her bones", obviously aware of Tessa's feeling for him. But in the next episode when Tessa again found herself in his bedroom, Melissa was there and she handcuffed Tessa to herself to keep her from sneaking into his room. She is a very strict person who doesn't take nonsense from anyone, especially her subordinates.
Despite all this, Melissa does have a good heart. She is good friends with both Kaname and Tessa, even having access to the latter's office, though she is not above using this to her advantage. She also acts as an older sister figure to her subordinates despite her drill sergeant attitude, and is even nicknamed "Big Sis" by Kurz.