Official Art of Kodama. Source
Kodama in Japanese can mean Echo; tree spirit or tree and rocks spirit or even small ball.
A school student (?) of unknown grade.
Kodama (こだま) is the protagonist of the Yume Nikki fangame Hana no Chiruramu (花の散るらむ).
Kodama has long black/dark gray hair tied back in a braid with a red hair rubber band. She wears a blue and white seifuku (Japanese school uniform) with long sleeves and a red neckerchief. Her shoes are brown and made of leather, they appear to be a part of her school uniform.
Kodama is apparently a school student. She dreams while resting her head on her desk, in an empty classroom which she refuses to leave. It is unknown she had secluded herself inside of it, or why she chose a classroom as her discreet sleeping/dreaming place. She also keeps her bag and notebook there.
There is no certain way of knowing at what time Kodama picked out to seclude herself in an empty classroom. As there are no other people in the classroom except for her, it may be she came to school too early or stayed there until everyone was gone, or even had spent a night in there. It could be an unused classroom she's using.