Who is Min's Wife, Ajima from A Single Shard and what is their importance?

Min's Wife, Ajima, serves Tree-ear his lunch each day, and even provides him
with warm clothes when winter approaches. Over time, Tree-ear and Min's wife develop a close relationship, she even encourages him to call her Ajima, a name that is like aunt and is reserved for highly respected adult family members. When Tree-ear returns from Songdo, Ajima gives him the name Hyung-pil and asks him to live with her and Min, as their adopted son.