MB

Unknown Miscellaneous Subject 5 is a new character featured in the Metroid: Other M trailer. She appears towards the end, in the segment where the "Living body arms development lab" is introduced. Just as Samus finishes entering her password into the screen to unlock the entrance, she spots the woman wearing a lab coat, who is startled by Samus' presence. The trailer ends with Samus introducing herself and the woman slowly looking up (presumably at Samus). This woman is not another Samus but a "very, very important character". 

The woman has long blonde hair with a hairclip on the left side of her head.