Natsuko Kawaguchi

川口 夏子,

Sister of the Machine Gun Brothers. Natsuko was a childhood friend of Kanta and a crybaby (according to him). She has not been in contact with Kanta and her brothers after leaving to work for the Oasis Government, where she has risen to the rank of captain. She is a proficient hand-to-hand combatant and the current idol of Kosuna. (from Wikipedia)