Master Sergeant Karen Sonomiya is a genius with an IQ of 170 and is an authority on mechanics. She is a university graduated girl at the age of 16 yrs old. She has trouble talking to boys, as she can be quite shy around them. She has a mild crush on Takumi. Karen also enjoys writing letters to her older brother who works just outside the base and loves him very much.
She is voiced by Saori Gotō.