Don’t let her cute looks fool you. Yoko is an extensive wielder of firearms, including the long range sniper rifle she’s holding in the image. She is the mature and rational member of the group, though she badmouths Kamina on occasion.
Yoko also loves children and is seen as a teacher named “Yomako” by the end of the series.
Nice pose, and her boots are pretty cute. I had no idea who this was until I searched the internet for more information. Thanks to Cosholics Cafe for the photo!