Nire's artwork (Source)
にれ = elm (?)
Nire has chin-length grayish-pink hair. She wears a light pink dress as well as a blue jacket over it. She also wears purple shoes. Nire wears a set of black headphones in the real world, although she doesn't wear them in the dream world.
Little can be said about Nire's personality as she does not talk in the game. What type of personality she has is left to the player's interpretation.
The menu mentioning her as somniphobic means that she fears falling asleep, although it is not yet known why or how this fear developed.
As the game is in an early stage at present, little is known about Nire's past or why she doesn't want to leave her apartment.
An interesting thing to note is that Nire wears headphones while she is awake, but she is not shown wearing them in the dream world. It could be possible that she wears the headphones to help her sleep (by either listening to music or wearing them to block out noise).