Nina is a member of the current Sleeping Forest led by Kilik.
Nina originally appears as a muscular man in dark, tight fitting clothes, however, she is actually appears as a petite woman with shoulder length hair and sporting a tight body suit that appears to help her sync with her AT suit. She is often seen talking with the unnamed male.
Personality-wise, Nina is shown to be very in-tune with others' thoughts and even their AT tricks. She provides an insightful analysis of Kilik's Gaia Road techniques and playfully discusses his battle strategies, commenting that she would probably use the same tactics if she were in his position. This attitude earns her a level of disdain from Ume.
Nina appears to be the equivalent of the Rumble Queen for Sleeping Forest.
Added by Dynasty 07
By opening her AT suit she is able to utilize a defensive move similar to Yoshitune's Rumble Wall.
Out of all of the regalia seen thus far, Nina's is easily the largest, dwarfing even Nue's armored Thunder Regalia. She has grown so accustomed to using it that she rarely leaves it, as is implied when she tells Kilik about "when she used to live on the ground".